The researchers synthesized HKUST-1 at room temperature from copper acetate and trimesic acid in an ethanol-water mixture, then opened its clogged pores using two different activation strategies. One sample, labeled HT, was heated at 100 degrees Celsius under vacuum for 24 hours. The other, labeled DCM, was repeatedly soaked in dichloromethane and dried over seven cycles. Because solvent molecules trapped inside the framework normally block the coordinatively unsaturated copper sites that drive catalysis, the choice of activation method matters enormously, and the team wanted a direct, like-for-like comparison that the literature rarely provides.

Characterization revealed that the two routes leave distinct fingerprints. Powder X-ray diffraction showed that heat treatment preserved the crystalline HKUST-1 framework, while solvent exchange reduced crystallinity and shifted peaks, a sign that capillary forces during evaporation had partially collapsed the structure. Nitrogen sorption measurements confirmed the consequence: the HT sample retained a surface area of 360 square meters per gram, whereas the DCM sample fell to 96 square meters per gram. X-ray photoelectron spectroscopy showed both samples contain a near-equal mix of Cu+ and Cu2+ states, a mixed valency that facilitates charge transfer, along with oxygen vacancies that are more prominent in the heat-treated material.

Photocatalytic tests used 10 milligrams per liter of methylene blue and a modest catalyst dose of 0.25 grams per liter under 100 milliwatts per square centimeter of simulated sunlight. The results were strikingly pH-dependent. In acidic solution, HT removed only about 53 percent of the dye in 180 minutes and DCM about 47 percent, because few hydroxide ions are available to form the reactive hydroxyl radicals that do the chemical heavy lifting. At neutral pH the efficiencies climbed to 93 percent for HT and 74 percent for DCM. Under basic conditions, degradation accelerated dramatically, with HT destroying 99.04 percent of the dye in just 60 minutes and DCM reaching 98.72 percent.

To identify the active species, the team added radical scavengers. Isopropyl alcohol, which mops up hydroxyl radicals, slashed degradation to roughly 23 to 27 percent, while EDTA, which traps holes, actually improved performance. Combined with cyclic voltammetry measurements of the band edges, this confirmed that hydroxyl radicals generated by valence-band holes oxidizing water are the dominant degrading agents, since the conduction band sits too positive to reduce oxygen to superoxide. Electrochemical impedance spectroscopy added another piece of evidence: the HT electrode showed lower charge-transfer resistance than DCM, meaning photogenerated electrons and holes separate and migrate more efficiently, suppressing the recombination that cripples many photocatalysts.

The most dramatic result came from destroying the framework altogether. Annealing HKUST-1 at 400 degrees Celsius converted it into a copper metal oxide, labeled CMO, composed of roughly spherical nanoparticles averaging 19 nanometers with rough, porous surfaces. This transformation collapsed the band gap from about 3.7 electronvolts in the parent MOF to just 1.41 electronvolts, allowing the oxide to absorb light across nearly the entire ultraviolet-visible spectrum. The payoff was speed: CMO degraded 98.80 percent of methylene blue within only 30 minutes at pH 12, with a pseudo-first-order rate constant of 143.52 x 10^-3 per minute, far outpacing the parent framework, and it still achieved 68.73 percent degradation in acidic conditions where the MOFs struggled.

Recyclability tests over six cycles showed efficiency losses of roughly 12 to 13 percent for all three catalysts, an acceptable decline attributable to gradual loss of active sites. Notably, post-cycling X-ray diffraction revealed that the HT and DCM frameworks partially hydrolyze under alkaline conditions, forming new copper-trimesate phases, whereas the CMO pattern remained essentially identical to the fresh catalyst. The monoclinic CuO phase resists both hydrolysis and photocorrosion, suggesting the derived oxide is the more durable option for repeated wastewater treatment duty.

Perhaps the most practically relevant part of the study concerns mixed pollutants, which most research ignores. When the cationic methylene blue and the anionic methyl orange were degraded together, the outcome depended sharply on pH. In acidic solution the catalyst surface becomes positively charged, attracting the anionic methyl orange, which was degraded 89.70 percent, while methylene blue removal dropped to 31.67 percent, inhibited by electrostatic repulsion and competitive adsorption. At neutral pH the split was 57.11 percent for methylene blue and 96.85 percent for methyl orange, and at pH 10 both dyes exceeded 97 percent removal within 180 minutes, turning the green mixed solution completely transparent.

Kinetic analysis of the binary system exposed another subtlety: the classical pseudo-first-order model that fits single-dye degradation broke down, with pseudo-second-order kinetics providing better fits in most cases. This deviation reflects the competing adsorption and reaction of two dyes on the same surface, a warning that multicomponent effluents cannot be predicted from single-pollutant studies alone. For engineers designing real treatment systems, the message is that pH can be used as a dial to select which dye is destroyed first, or to eliminate both simultaneously.

Taken together, the study delivers a comprehensive map linking activation strategy, physicochemical properties, and photocatalytic performance for copper-based materials. It shows that a simple, chemical-free activation choice such as vacuum heating can outperform solvent exchange by preserving porosity, and that converting a MOF into its oxide trades surface area for a dramatically narrower band gap, faster kinetics, and superior stability. As industries seek sustainable alternatives to Fenton chemistry, which works only in narrow acidic windows and generates metal sludge, these sunlight-driven copper catalysts, active across pH 2 to 12 and reusable over multiple cycles, offer a compelling blueprint for the rational design of next-generation water purification materials.

Subject of Research: Photocatalytic degradation of organic dyes using activated HKUST-1 metal-organic framework and its derived copper oxide

Article Title: Photocatalytic degradation of single and binary dyes using activated HKUST-1 and its derived copper oxide

Article References: Sonia, Singh, V., Yarramaneni, S., & Singh, V. (2026). Photocatalytic degradation of single and binary dyes using activated HKUST-1 and its derived copper oxide. Discover Chemistry, 3(1), Article 522. https://doi.org/10.1007/s44371-026-00977-y

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00977-y

Keywords: HKUST-1, metal-organic framework, photocatalysis, copper oxide, methylene blue, methyl orange, wastewater treatment, band gap, hydroxyl radicals, dye degradation, pH-dependent selectivity, MOF-derived catalysts

The research team, led by Xiaoyan Liu and Yirong Wang of the School of Minerals Processing and Bioengineering at Central South University in Changsha, China, together with colleagues including corresponding author Hongchang Liu and Zhenyuan Nie, designed a 42-day experiment with a 2 × 2 × 2 factorial structure. That means they independently varied three factors: the mineral composition, with and without pyrite mixed into the stibnite; the light conditions, running parallel treatments under illumination and in complete darkness; and the biological conditions, with and without a community of acidophilic microorganisms of the kind that thrive in acidic mine drainage. By crossing these factors, the team could separate the contribution of each variable and, crucially, detect the interactions between them that simpler experiments would miss.

The analytical arsenal deployed in the study was correspondingly broad. The researchers tracked solution chemistry over the entire incubation, examined the chemical composition of mineral surfaces using X-ray photoelectron spectroscopy, characterized the structure of the microbial communities that developed in each treatment, measured the electrochemical behavior of the mineral pairs, and monitored signals of hydroxyl radicals, the ferociously reactive species denoted ·OH that can oxidize sulfide minerals and their dissolved products. This combination allowed the group to link macroscopic dissolution rates to molecular-scale interfacial processes, a connection that has long been difficult to establish for mixed sulfide mineral systems in mining environments.

The headline result concerns galvanic coupling. When two minerals with different electrochemical potentials are in electrical contact in an electrolyte, they behave like a short-circuited battery: the mineral with the lower rest potential becomes the anode and dissolves preferentially, while the more noble mineral acts as the cathode. Electrochemical analyses in the study confirmed that in pyrite–stibnite mixtures, pyrite assumes the cathodic role and stibnite the anodic one. In practical terms, the presence of pyrite accelerates the anodic dissolution of stibnite, effectively wiring the antimony ore into a corrosion cell that keeps pushing electrons out of the stibnite lattice. The authors identify this pyrite–stibnite galvanic coupling as the primary electrochemical process driving stibnite biodissolution in their experiments, which explains why pyrite emerged as the dominant factor among all the variables tested.

The microbial dimension of the study adds a second, complementary layer to the mechanism. Under biotic conditions, pyrite did more than serve as a passive cathode. Its dissolution released iron and sulfur species into solution, and these products sustained microbial iron and sulfur cycling. Acidophilic microorganisms, notably iron oxidizers of the kind well known from bioleaching systems, oxidize ferrous iron to ferric iron, and ferric iron is itself a powerful oxidant that attacks sulfide minerals. By feeding this cycle, pyrite-derived Fe and S species enabled continuous Fe3+ regeneration, maintaining an oxidizing environment that supported ongoing stibnite dissolution even as the experiment progressed over six weeks. In other words, the microbes and the minerals form a self-reinforcing loop: pyrite supplies the chemical fuel, microbes regenerate the oxidant, and stibnite pays the price by dissolving.

Light, the third experimental variable, played a more subtle but chemically elegant role. Pyrite is a semiconductor, and illumination can promote electrons across its band gap, altering the way charge transfers at the mineral–water interface. The X-ray photoelectron spectroscopy results quantify this effect vividly. On mineral surfaces exposed to light, the relative proportion of sulfate, the fully oxidized end product of sulfide oxidation, rose from 29.80 percent in the dark to 63.89 percent under illumination. Meanwhile, residual sulfide on the surfaces fell from 50.33 percent to just 15.55 percent. These numbers indicate that light substantially accelerated the surface oxidation of the sulfide minerals, shifting the interfacial chemistry toward more complete oxidation. The study concludes that light mainly affected interfacial electron transfer rather than acting as the primary driver of dissolution in its own right.

Accompanying the photochemical effect was a change in reactive oxygen chemistry. The pyrite-bearing biotic system exposed to light displayed stronger hydroxyl radical signals than its dark counterpart. Hydroxyl radicals are among the most potent oxidants in aqueous chemistry, and previous work has shown that pyrite surfaces can generate them through reactions involving oxygen, water, and intermediate hydrogen peroxide. The new findings tie this radical production into the broader dissolution picture: in systems containing both pyrite and stibnite under illumination, interfacial electron transfer and radical-mediated oxidation reinforce one another, deepening the oxidative transformation of the mineral surfaces and, by extension, the mobilization of antimony.

Why does this matter beyond the laboratory? Antimony contamination around mining districts is a serious environmental and public health issue, and the mobility of antimony in water depends strongly on its oxidation state and speciation. Understanding what controls the rate at which stibnite weathers is therefore essential for predicting how antimony spreads from mine waste into rivers, sediments, and groundwater. The study’s finding that a seemingly inert companion mineral can electrochemically accelerate ore dissolution means that risk assessments based on stibnite alone may substantially underestimate release rates in pyrite-rich ores, which are common in nature. The work also resonates with earlier research showing that pyrite-induced hydroxyl radicals can oxidize antimonite, the reduced form of antimony, hinting that the galvanic and radical pathways may jointly shape antimony speciation in the field.

The research also carries implications for the industrial side of the antimony story. Bioleaching, the use of acidophilic microbes to extract metals from sulfide ores, relies on precisely the same chemistry that mobilizes antimony in the environment. If pyrite–stibnite galvanic coupling is the dominant dissolution mechanism, then process designers could exploit it deliberately, tuning mineral blends, ferric iron regeneration, and even illumination to enhance metal recovery from refractory antimony ores and metallurgical residues. Conversely, in remediation scenarios, suppressing the galvanic contact or interrupting microbial iron cycling could slow antimony release from tailings. The same electrochemical insight thus cuts in two directions, offering both a hazard model and a process lever.

What makes the study conceptually satisfying is its synthesis of three traditionally separate perspectives on sulfide mineral weathering: electrochemistry, microbiology, and photochemistry. Rather than treating these as competing explanations, the factorial design reveals them as nested layers of one system. Pyrite sets the electrochemical stage by forming a corrosion couple with stibnite; the microbial community maintains the oxidizing atmosphere by cycling iron and sulfur species; and light modulates the rate of interfacial electron transfer while amplifying hydroxyl radical production. For anyone tracking the environmental fate of antimony, from mine-site hydrologists to geochemists modeling critical raw material flows, the message is that the invisible wiring between minerals, microbes, and photons deserves as much attention as the ore itself. The full study is available in Environmental Geochemistry and Health under DOI 10.1007/s10653-026-03484-2.

Subject of Research: Pyrite-driven galvanic and microbial mechanisms controlling stibnite biodissolution under light and dark conditions

Article Title: The influence mechanism of pyrite on the biodissolution of stibnite under light/darkness conditions

Article References: Liu, X., Wang, Y., Wu, D., Chen, L., Liu, H., Yang, W., Muhammad, A., Lai, J., & Nie, Z. (2026). The influence mechanism of pyrite on the biodissolution of stibnite under light/darkness conditions. Environmental Geochemistry and Health, 48(14), Article 581. https://doi.org/10.1007/s10653-026-03484-2

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03484-2

Keywords: antimony, stibnite, pyrite, galvanic corrosion, biodissolution, acidophilic microorganisms, iron cycling, sulfur cycling, hydroxyl radicals, mine drainage, photochemistry, Environmental Geochemistry and Health

The team’s strategy rests on the single-source precursor approach, a method in which a single molecule carries both the metal and the chalcogenide needed for the final semiconductor. In this case, the precursors are lead(II) dithiocarbamate complexes, in which a sulfur-rich dithiocarbamate ligand binds the lead center while an organic substituent hangs off the ligand’s nitrogen atom. Because the lead and sulfur are already bonded within one molecule, decomposition can deliver both elements to the growing nanocrystal in a controlled, stoichiometric fashion, often at lower temperatures and with cleaner chemistry than routes that mix separate lead and sulfide reagents. The dithiocarbamate family has a long pedigree here, having served as single-source precursors to binary, ternary and quaternary metal sulfides across the nanomaterials literature.

What distinguishes the new study is the systematic comparison of three newly synthesized complexes that differ only in the organic moiety attached to nitrogen. Complex 1 carries an N-hexyl-N-(1H-indole-3-yl-methyl) substituent, pairing a six-carbon chain with an indole ring. Complex 2 combines an N-dodecyl group, a long twelve-carbon tail, with an N-(4-dimethylaminobenzyl) aromatic unit bearing a dimethylamino group. Complex 3 features an N-(2,4-dichlorobenzyl)-N-(2-phenylethyl) arrangement, in which a chlorinated benzyl group sits alongside a two-carbon phenethyl chain. All three were prepared and characterized by infrared and nuclear magnetic resonance spectroscopy, using both proton and carbon-13 measurements, together with elemental analysis. The spectral data confirmed that in every complex the dithiocarbamate ligand coordinates to lead in a bidentate fashion through both sulfur atoms, the classic chelating mode that stabilizes these molecules until they are deliberately decomposed.

To convert the precursors into nanomaterials, the researchers used a reflux method in which each complex was decomposed in the presence of ethylenediamine, which acted as a capping agent. Capping agents adsorb onto the surfaces of growing nanocrystals and moderate their growth, influencing both size and shape. The products, labeled PbS-1, PbS-2 and PbS-3 according to the precursor from which they came, were all established as single-phase lead sulfide with a face-centered cubic crystalline structure, the thermodynamically favored galena-type lattice of PbS. That all three precursors yielded the same phase is significant: it means the organic group was not changing what the material is, but rather how it is built, which is precisely the kind of orthogonal control synthetic chemists prize.

The differences emerged when the team examined morphology by field emission scanning electron microscopy. The N-bound organic moiety in complexes 1 through 3 significantly influenced the shape and architecture of the resulting lead sulfide nanoparticles, with each precursor producing its own characteristic morphology. This structure-directing effect is understood to arise from the way the precursor’s organic shell interacts with the reaction medium and with the nascent crystal surfaces during decomposition. Long alkyl chains, aromatic rings, halogen substituents and heterocycles each impose different steric demands, solubilities and surface affinities, and those differences propagate into the geometry of the final nanocrystals. Because photocatalysis is a surface-driven process, morphology is not cosmetic; it determines how much active surface is exposed to light and to the pollutant molecules that must adsorb onto it.

Optical properties were probed by ultraviolet-visible diffuse reflectance spectroscopy, a technique well suited to powdered samples that scatter light. The spectra allowed the team to characterize the optical band gaps of the three nanoparticle samples, which reflect the electronic structure of the semiconductor and govern which wavelengths of light the material can absorb to generate charge carriers. Lead sulfide is a famously versatile semiconductor in this respect: bulk PbS has a narrow band gap of about 0.4 electron volts, but quantum confinement in nanoscale crystals can push the effective gap into the visible range, a property exploited in lead sulfide quantum dot solar cells and infrared photodetectors. In the present work, the optical behavior of the three samples tracked their structural and morphological differences, completing the chain of causation from molecular precursor to functional material.

The practical payoff came in photocatalysis tests targeting methylene blue, a thiazine dye widely used as a model pollutant and a genuine environmental concern in its own right, given its documented toxicity and persistence in wastewater from textile, paper and leather industries. Under ultraviolet irradiation, all three PbS catalysts degraded aqueous methylene blue, but their efficiencies differed markedly. PbS-3, the nanoparticles derived from the dichlorobenzyl and phenethyl-substituted precursor, was the standout, achieving 92 percent degradation of the dye. The comparison across the three catalysts demonstrates that the precursor’s organic chemistry, transmitted through morphology and surface structure, directly controls catalytic performance.

The researchers did not stop at a single measurement. They systematically examined how reaction parameters affect degradation, varying the pH of the solution, the initial dye concentration and the photocatalyst dose. These variables matter for any real deployment: pH alters both the surface charge of the catalyst and the ionization state of the dye, dye concentration determines whether the process is limited by light penetration or by available active sites, and catalyst loading must balance surface area against light scattering and particle aggregation. The team also tested recyclability, and the nanocatalysts performed well over four consecutive degradation cycles, an essential criterion for a material that must be recovered and reused to be economically and environmentally viable. A catalyst that loses activity after one run merely converts a water problem into a solid waste problem.

Mechanistically, radical scavenger experiments identified hydroxyl radicals as the dominant reactive species responsible for dye degradation. This finding fits the standard photocatalytic picture: when photons excite electrons from the valence band of the semiconductor to its conduction band, they leave holes behind. The holes can oxidize water or hydroxide ions at the surface to generate hydroxyl radicals, while the excited electrons can reduce dissolved oxygen to superoxide and, downstream, to further reactive oxygen species. Hydroxyl radicals are among the most aggressive oxidants in aqueous chemistry, capable of tearing apart the conjugated chromophore structures that give dyes their color and their persistence. Knowing which species dominates allows future work to focus on maximizing its production, for example by engineering surfaces and band alignments that favor hole-driven hydroxyl generation.

Beyond the immediate results, the study reinforces a broader lesson in nanoscience: the precursor is not just a source of atoms but a template for the material’s final form. By choosing the N-bound organic moiety, chemists gain a molecular-level dial for morphology, and through morphology, for optical response and catalytic efficiency. The Annamalai University team’s three complexes show that this dial can be turned with ordinary synthetic chemistry, spectroscopic verification and a straightforward reflux decomposition, without exotic equipment. As industries from textiles to leather grapple with dye-laden effluent, and as advanced oxidation processes increasingly pair with biological treatment to detoxify wastewater, catalysts like PbS-3 suggest a path in which the design work happens at the molecular drawing board, long before the catalyst ever meets a polluted river. The remaining challenges, scaling synthesis, confirming performance on real industrial effluents rather than model dyes, and managing the environmental footprint of lead-based materials, are substantial, but the demonstration that a single organic substituent can swing degradation efficiency so decisively is a compelling argument for precursor-first nanomaterial design.

Subject of Research: Synthesis of lead sulfide nanoparticles from lead(II) dithiocarbamate single-source precursors and their photocatalytic degradation of methylene blue

Article Title: Influence of N-bound organic moiety in lead(II) dithiocarbamates on morphology and optical properties of photocatalytically active lead sulfide nanoparticles

Article References: Gokul, G., Uthiravel, V., & Thirumaran, S. (2026). Influence of N-bound organic moiety in lead(II) dithiocarbamates on morphology and optical properties of photocatalytically active lead sulfide nanoparticles. Journal of Nanoparticle Research, 28(10), Article 259. https://doi.org/10.1007/s11051-026-06777-w

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06777-w

Keywords: lead sulfide, dithiocarbamate, single-source precursor, nanoparticles, photocatalysis, methylene blue, dye degradation, hydroxyl radicals, morphology, band gap, wastewater treatment, nanomaterials

The material at the heart of the study, published in the Journal of Nanoparticle Research, is a molecularly imprinted form of bismuth ferrite, abbreviated I-BFO. Bismuth ferrite, or BiFeO3, is a perovskite-type semiconductor that has long attracted attention in photocatalysis because it absorbs a substantial portion of visible light, making it suitable for solar-driven chemistry. Its weakness, shared by most conventional photocatalysts, is a lack of discrimination. In a real wastewater stream, dozens of organic compounds compete for the catalyst’s surface, and a non-selective material wastes its oxidative power on whatever happens to be nearby. The Chinese team’s solution was borrowed from a technique that immunology and analytical chemistry have used for decades: molecular imprinting, in which a template molecule is used to cast custom-shaped recognition cavities into a surrounding matrix.

The imprinting process works much like making a key mold. Ciprofloxacin molecules are introduced during the synthesis of the catalyst, and as the bismuth ferrite framework forms around them, it develops cavities whose size, shape and chemical functionality complement the antibiotic. When the template molecules are subsequently removed, they leave behind a landscape of molecular footprints on the catalyst surface. These cavities preferentially re-adsorb ciprofloxacin, positioning the target molecule in intimate contact with the catalytically active sites before light-driven degradation begins. The result is a catalyst that concentrates its chosen substrate at the very locations where reactive oxygen species are generated, rather than letting those powerful oxidants dissipate on irrelevant organic matter.

The performance gains reported by the team, led by corresponding authors Jie Jin and Ziyang Lu, are substantial. Compared with pristine, non-imprinted bismuth ferrite, the imprinted catalyst achieved a 2.52-fold increase in the degradation rate of ciprofloxacin. That acceleration is not merely a matter of faster adsorption; it reflects the tighter coupling between molecular recognition and photocatalytic oxidation. When the target molecule is held within a complementary cavity, the photogenerated oxidants that break it apart are produced in its immediate vicinity, shortening the diffusion pathways that normally limit reaction rates and reducing the chance that intermediates escape into solution before complete mineralization.

Selectivity was tested directly in competitive degradation experiments, where ciprofloxacin had to contend with tetracycline, another common antibiotic with a very different molecular architecture. The imprinted catalyst consistently favored ciprofloxacin, degrading it preferentially over tetracycline and registering a selectivity coefficient of 1.79 relative to the pristine material. In practical terms, this means the catalyst can operate in a mixed-pollutant environment and still direct its oxidative capacity toward the compound it was designed to recognize. For treatment engineers, that kind of discrimination is invaluable: it allows a targeted catalyst to be deployed against a specific problematic contaminant without being poisoned or distracted by the chemical noise that characterizes real municipal and industrial effluents.

Durability is the other half of the story, and here too the imprinted material performed well. Across five successive degradation cycles, the catalyst retained approximately 90.0 percent of its initial efficiency, a figure that speaks to both the robustness of the bismuth ferrite framework and the stability of the imprinted cavities. Recyclability has long been a stumbling block for advanced photocatalysts, many of which suffer from photocorrosion, leaching of metal ions, or fouling of their active surfaces after only a few uses. A catalyst that can be recovered and reused with minimal loss of activity is far more attractive for continuous water treatment operations, where replacement costs and material losses quickly erode any laboratory-scale advantage.

To understand which chemical species were actually doing the work of destruction, the researchers carried out radical scavenging experiments, in which specific quenchers are added to intercept particular reactive intermediates. The results pointed to photogenerated holes and hydroxyl radicals as the primary reactive species governing ciprofloxacin degradation. Photogenerated holes are the positively charged vacancies left behind when a semiconductor absorbs light and promotes electrons to its conduction band; they are powerful oxidants in their own right and can directly attack organic molecules adsorbed on the catalyst surface. Hydroxyl radicals, meanwhile, are among the most aggressive oxidants known in aqueous chemistry, capable of stripping hydrogen atoms and adding across double bonds in organic pollutants. The identification of these two species as the dominant actors provides a mechanistic picture that future researchers can build upon when optimizing related systems.

The broader significance of the work lies in how it addresses two chronic limitations of photocatalytic water treatment at once: selectivity and charge dynamics. The authors frame the enhancement of charge separation efficiency as a central objective in the field, because when electrons and holes recombine inside a semiconductor instead of reaching the surface, their oxidative and reductive potential is simply lost as heat. Molecular imprinting contributes indirectly to this challenge as well, by ensuring that adsorbed target molecules are positioned to consume the charge carriers as soon as they arrive at the surface, effectively giving the photogenerated holes and radicals something productive to do before recombination can occur. The study thus sits within a wider research effort, visible across the team’s own recent publications, to engineer photocatalytic materials whose surfaces are as thoughtfully designed as their bulk electronic structures.

The environmental context makes the advance timely. Global ecological analyses have shown that concentrations of ciprofloxacin in the world’s rivers correlate with the prevalence of fluoroquinolone resistance in Escherichia coli, tying water quality directly to the trajectory of the antimicrobial resistance crisis. Conventional approaches, from adsorptive membranes to advanced oxidation processes, can remove or destroy antibiotics, but they typically do so without preference, consuming energy and reagents on the full cocktail of contaminants present. A selective photocatalyst that runs on light and targets the most problematic compound in the mixture represents a more surgical intervention, one that could be combined with existing treatment trains to polish effluents before discharge or to treat concentrated waste streams at their source, such as hospital effluent and pharmaceutical manufacturing wastewater.

Challenges remain before imprinted photocatalysts like I-BFO reach real-world deployment. Scaling up the imprinting synthesis while maintaining uniform cavity quality, demonstrating performance in genuinely complex environmental water matrices with their humic substances and competing ions, and integrating the catalyst into continuous-flow reactors are all steps that lie ahead. Yet the experimental foundation laid by the Jiangsu University team is a meaningful one. By fusing the molecular recognition of imprinting with the visible-light activity of bismuth ferrite, and by demonstrating both a 2.52-fold rate enhancement and a clear selectivity advantage in competitive settings, the researchers have shown that photocatalysis can be taught to tell its targets apart. In a world where the smallest concentrations of a single drug can reshape microbial ecosystems, that ability to aim, rather than simply blast, may prove to be exactly what environmental remediation has been waiting for.

Subject of Research: Molecularly imprinted bismuth ferrite photocatalysis for selective degradation of ciprofloxacin in wastewater

Article Title: Targeted photodegradation of ciprofloxacin on imprinted bismuth ferrite with improved catalytic performance

Article References: Onwubiko, J. S., Xu, Y., Li, X., Cheng, Y., Tang, L., Liu, X., Jin, J., & Lu, Z. (2026). Targeted photodegradation of ciprofloxacin on imprinted bismuth ferrite with improved catalytic performance. Journal of Nanoparticle Research, 28(10), Article 258. https://doi.org/10.1007/s11051-026-06781-0

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06781-0

Keywords: photocatalysis, bismuth ferrite, molecular imprinting, ciprofloxacin, antibiotic pollution, wastewater treatment, selective degradation, hydroxyl radicals, charge separation, environmental remediation, nanomaterials, water purification

A new comprehensive review by Ryma Merdoud and Vivek V. Ranade, published in Case Studies in Chemical and Environmental Engineering, tackles this problem by systematically analysing one of the most promising advanced oxidation technologies: hydrodynamic cavitation coupled with hydrogen peroxide. Rather than cataloguing efficiencies, the authors build a quantitative framework designed to make results from different laboratories genuinely comparable, using methyl orange—a sulfonated monoazo dye monitored by its distinctive absorption at 465 nanometres—as the analytical probe across more than 30 peer-reviewed studies published since 2016. The central insight is deceptively simple but transformative for the field: degradation performance must be measured per pass through the cavitation device, not per unit of time.

The physics behind the technology is dramatic. When liquid is forced through a constriction such as an orifice plate, venturi, or vortex diode, the local pressure can drop below the vapour pressure, causing the liquid to tear open and form clouds of vapour bubbles. When these bubbles subsequently implode, the Rayleigh–Plesset equations predict localised temperatures near 5,000 kelvin and pressures around 500 atmospheres at the bubble centre. Under these extreme conditions, water vapour trapped inside the collapsing bubble dissociates homolytically into hydroxyl radicals and hydrogen atoms. Hydroxyl radicals are ferocious oxidants, with a standard reduction potential of 2.80 volts, and they attack aromatic compounds at near-diffusion-controlled rates of 10^8 to 10^10 per molar per second. Crucially, some of these radicals recombine to form hydrogen peroxide in situ, accumulating over successive passes as a latent oxidant reservoir that later collapses can reactivate—a self-amplifying loop that forms the mechanistic core of the hybrid process.

Externally added hydrogen peroxide plays a double-edged role. At low concentrations, the energy of bubble collapse splits it into two additional hydroxyl radicals, amplifying the oxidative flux. At high concentrations, however, the same molecule becomes a scavenger, consuming hydroxyl radicals to form the far weaker perhydroxyl radical and water. This dual chemistry gives rise to three distinct operational regimes that the review defines with data-derived boundaries. Below roughly 0.003 percent hydrogen peroxide by volume, the system is under-dosed and synergy coefficients hover between 1.1 and 2.0. In the optimal window—about 0.005 to 0.015 percent depending on device type—synergy coefficients climb to between 2.0 and 4.8, meaning the combined process degrades the dye up to nearly five times faster than the sum of its parts. Above roughly 0.05 percent, scavenging dominates and the coefficient falls to one or below, with antagonism confirmed experimentally at 1 percent by volume.

The methodological heart of the review is the per-pass rate constant, which measures the fraction of pollutant degraded in a single transit through the cavitation device. The authors demonstrate that the conventional time-based rate constant is contaminated by a geometric artefact: because it scales inversely with the volume-to-flow-rate ratio of the recirculating tank, two chemically identical experiments with different tank sizes will report different rate constants. Synergy coefficients computed from such time-based values therefore embed a geometric multiplier rather than a chemical signal. By converting all published data to per-pass form, the review compiles a dataset in which vortex and swirl devices achieve per-pass constants of 0.022 to 0.050 per pass, venturi systems 0.018 to 0.050, and orifice plates 0.009 to 0.032—a hierarchy confirmed independently by coumarin dosimetry showing vortex diodes generate 1.5 to 2 times more hydroxyl radicals per unit energy than matched orifice and venturi devices.

The synergy analysis yields a strikingly consistent picture. Across six studies meeting the highest data-quality grade, per-pass enhancement factors and synergy coefficients agree to within 2 percent, validating the assumption that hydrogen peroxide alone is essentially inert under the dilute conditions reviewed. The median synergy coefficient in the optimal regime is approximately 3.0, with vortex devices clustered at the top (3.3 to 4.8), venturi systems in the middle (2.5 to 3.5), and orifice plates at the bottom (2.0 to 2.8). Operating parameters modulate these values substantially: raising pH from 3 to 7 cut synergy by 60 percent in one venturi study by unleashing carbonate scavenging, while increasing pressure beyond the optimum shifted systems toward the scavenging regime at fixed peroxide dose. The authors recommend dosing by molar ratio—20 to 100 moles of peroxide per mole of dye—rather than by absolute concentration.

Benchmarking against rival hybrid processes reveals why the simple peroxide system is attractive. Hydrodynamic cavitation paired with Fenton chemistry achieves higher chemical oxygen demand removal (50 to 60 percent) but demands pH below 3, generates iron sludge, and faces discharge limits on iron. Ozone combinations decolourise rapidly but consume 10 to 15 kilowatt-hours per kilogram of ozone, require off-gas destruction, and risk forming carcinogenic bromate in bromide-containing effluents. Ultraviolet-based hybrids reach synergy coefficients near 8 but suffer lamp costs and turbidity limitations. Adding titanium dioxide photocatalysis to the cavitation–peroxide system pushes synergy to 9.2—the highest rigorously quantified value in the dataset—though this result rests on a single bench-scale study. For most scenarios, the review concludes, cavitation with peroxide offers the best balance of performance, simplicity, and cost, with specific energy consumption of 2 to 10 kilowatt-hours per cubic metre and operating expenses of roughly 0.8 to 3 dollars per cubic metre.

Scale-up emerges as the field’s central unresolved challenge. Experimental data spanning a 200-fold flow-rate range for vortex devices show that per-pass performance declines with increasing device size, approaching a finite asymptotic value as cavitation extent and specific energy dissipation dilute—a trend corroborated by computational fluid dynamics and machine-learning analyses of radical dosimetry. Synergy coefficients, the authors caution, should only be compared between reactors of similar geometric scale. Energy utilisation efficiency imposes another ceiling: no more than 15 percent of pump energy converts into hydroxyl radical generation, with the rest lost as heat, viscous dissipation, and noise. Controlled aeration upstream of the device offers a partial remedy, boosting per-pass performance by 20 to 40 percent for a modest parasitic energy cost, though the benefit reverses if over-aeration cushions bubble collapse.

Perhaps the review’s most consequential contribution is its proposed minimum reporting standard, a checklist requiring per-pass constants for each process component, volume-to-flow-ratio data, cavitation yield, residual peroxide measurements, chemical oxygen demand alongside decolouration, and at least one ecotoxicological assay. That last item addresses a sobering finding: decolouration is a poor proxy for safety. Hydrodynamic cavitation alone achieved 96 percent decolouration but only 12 percent mineralisation in one study, leaving colourless aromatic amines and short-chain acids in solution. Hybrid peroxide treatment roughly doubled mineralisation rates and cut acute toxicity measurably in Vibrio fischeri and seed germination assays. With fewer than 15 percent of reviewed studies testing real textile effluent, and long-term device erosion virtually uncharacterised, the authors argue that standardised, machine-readable reporting is the single most impactful step toward turning a decade of laboratory promise into predictable industrial practice for the dyehouses discharging billions of cubic metres of coloured wastewater worldwide.

Subject of Research: Hydrodynamic cavitation combined with hydrogen peroxide for the degradation of azo dye pollutants in wastewater

Article Title: Hydrodynamic cavitation–H 2 O 2 systems for azo dye degradation: Per-pass kinetics, synergy coefficients, and scale-up insights using methyl orange as a model pollutant

Article References: Merdoud, R., & Ranade, V. V. (2026). Hydrodynamic cavitation–H2O2 systems for azo dye degradation: Per-pass kinetics, synergy coefficients, and scale-up insights using methyl orange as a model pollutant. Case Studies in Chemical and Environmental Engineering, 14, Article 101480. https://doi.org/10.1016/j.cscee.2026.101480

Image Credits: AI Generated

DOI: 10.1016/j.cscee.2026.101480

Keywords: hydrodynamic cavitation, hydrogen peroxide, azo dyes, methyl orange, advanced oxidation processes, hydroxyl radicals, wastewater treatment, synergy coefficient, per-pass kinetics, scale-up, textile effluent, cavitation yield

The Fenton reaction is one of the oldest and most widely studied advanced oxidation processes in environmental engineering. By combining hydrogen peroxide with ferrous iron, it generates hydroxyl radicals, species denoted ·OH that are among the most powerful oxidants known, capable of ripping hydrogen atoms and electrons from nearly any organic molecule. In aqueous systems, Fenton chemistry is spectacularly effective. In soil, however, it has long underperformed, and the reason is fundamental: hydroxyl radicals are generated in the water that permeates soil pores, but petroleum hydrocarbons are hydrophobic. Medium and long chain alkanes, with carbon numbers typically above ten, partition strongly into the organic matter and oil phases of soil and away from the aqueous phase. The radicals, with lifetimes measured in microseconds and diffusion distances measured in nanometers, are consumed by water and by dissolved scavengers before they ever reach the target molecules. The result is what remediation scientists call ineffective consumption of hydroxyl radicals, an enormous waste of oxidant and a persistent bottleneck for in situ chemical oxidation.

The research team, led by Jinlan Xu and including Chongyue Guo, Xin Zhai, Jianan Dai, Hui Li, Lan Yang, Miaolin Liu, Xiang Li, and Yuhan Niu, approached this transport problem from a direction that few had quantified before: the intrinsic polarity of the soil matrix itself. Rather than trying to drag pollutants into the water with surfactants, they asked whether the water-borne radicals could be drawn into the soil. Their central insight is that soil is not a chemically uniform sponge but a heterogeneous surface whose affinity for polar species depends on the functional groups exposed on its organic matter. Soils rich in hydrophilic groups such as hydroxyl, carboxyl, and ether linkages present polar surfaces that can effectively pull polar radicals and oxidants out of solution and conduct them to the reaction sites where hydrocarbons adsorb.

To quantify this property, the researchers defined a polarity parameter, eta, calculated as the ratio of the integrated infrared spectral area of hydrophilic functional groups, specifically –OH, –COOH, and C–O–C stretching bands, to the proportion of humic acid in the soil. Fourier transform infrared spectroscopy, or FTIR, allowed them to track how these hydrophilic signatures changed across treatments, while excitation-emission matrix fluorescence spectroscopy, known as 3DEEM, resolved the composition of dissolved organic matter into humic and hydrophilic fractions. The team also introduced a metric they call the hydroxyl radical transfer ratio, an indirect indicator of how efficiently the radicals generated in the aqueous phase actually reach the soil matrix where the hydrocarbons reside. Together, these measurements allowed the group to link soil chemistry, radical transport, and pollutant destruction in a single quantitative framework.

The results were striking. As the soil polarity parameter eta was increased from 149.38 to 227.47, the hydroxyl radical transfer ratio climbed to 64.38 percent, and the total oxidation amount of petroleum hydrocarbons rose from 4,673 to 13,118 milligrams per kilogram of soil, an increase of 2.81 times. The effect was even more pronounced for the most recalcitrant fraction of the contamination: the total oxidation of middle and long chain alkanes increased from 2,816 to 9,555 milligrams per kilogram, a 3.39-fold enhancement. These are precisely the hydrocarbon fractions that conventional Fenton treatment leaves behind, the waxy, low-volatility chains that dominate aged spill sites and refuse to biodegrade quickly. FTIR analysis confirmed the physical basis of the effect, showing that the total integrated area of hydrophilic functional groups in the treated soils increased from 22.80 to 30.85, consistent with the hypothesis that enhanced soil hydrophilicity underpinned the improved radical delivery.

The fluorescence measurements added a second, equally important layer of mechanism. The 3DEEM spectra revealed that the polarity increase was driven by an increase in the content of hydrophilic components within the dissolved organic matter coupled with a decrease in the relative proportion of humic acid. Humic acid, the dark, aromatic workhorse of soil organic matter, is a notorious radical scavenger; its conjugated structures consume oxidants readily and can paradoxically protect pollutants from attack. By shifting the balance of organic matter away from humic material and toward hydrophilic components, the treatment simultaneously reduced wasteful radical quenching and increased the number of polar binding sites that transport oxidants toward hydrophobic contaminants. In effect, the researchers rewired the organic chemistry of the soil so that it funneled reactivity toward the pollutants rather than dissipating it.

What makes this study notable within the remediation literature is its reframing of the Fenton bottleneck as a mass transfer problem rather than a chemistry problem. Previous work by the same group and others had attacked the problem from multiple angles, including functionalized Fe/N co-doped biochars that mediate heterogeneous Fenton reactions at oil-water interfaces, oil-absorbing iron catalysts that bring the metal and the oxidant into direct contact with crude oil, and the inactivation of soil organic matter coupled with manganese mineral passivation to redirect oxidant distribution. Each strategy achieved oriented oxidation of hydrocarbons, but the new work isolates a single, tunable variable, soil polarity, and demonstrates a dose-response relationship between that variable and oxidation efficiency. This kind of mechanistic parsimony is rare in a field crowded with composite materials and multi-component processes, and it suggests a design principle that could be applied broadly: rather than engineering the oxidant or the catalyst, engineer the medium.

The practical implications are significant for the economics of soil remediation. Fenton treatment is already attractive because hydrogen peroxide is inexpensive and its byproducts are benign, but field applications routinely require high oxidant doses precisely because most radicals are wasted on water and natural organic matter. If raising the transfer ratio to roughly 64 percent allows comparable or greater contaminant destruction at a fraction of the oxidant loading, the cost per ton of treated soil could fall substantially. Moreover, because the polarity adjustment operates through the soil’s own organic matter composition rather than through persistent synthetic additives, the approach aligns with growing regulatory pressure for green and sustainable remediation technologies that leave soils fit for future ecological function. The study was supported by the Natural Science Foundation of China and Shaanxi Provincial research programs, reflecting the scale of petroleum contamination challenges in major oil-producing regions.

There remain, of course, questions that laboratory-scale batch studies cannot fully answer. Real field soils vary enormously in organic matter content, mineralogy, pH, and buffering capacity, and the eta parameter will need validation across that diversity before it can guide engineering design. The long-term stability of a polarity-adjusted soil, and whether repeated treatment cycles sustain the hydrophilic functional group inventory, will matter for multi-season remediation projects. Yet the conceptual contribution stands on its own: the fate of a hydroxyl radical in contaminated soil is decided not only by what it can oxidize but by where it can travel, and the journey from water to oily contaminant can be engineered through the polarity of the terrain itself. In a field long dominated by the search for stronger oxidants and better catalysts, this work is a reminder that sometimes the most powerful lever is the quiet chemistry of the ground beneath the spill.

Subject of Research: Soil polarity regulation to enhance Fenton oxidation of petroleum hydrocarbons via hydroxyl radical migration

Article Title: Efficient direct oxidation of medium/long chain petroleum hydrocarbons through migration of hydroxyl radicals by increasing soil polarity

Article References: Xu, J., Guo, C., Zhai, X., Dai, J., Li, H., Yang, L., Liu, M., Li, X., & Niu, Y. (2026). Efficient direct oxidation of medium/long chain petroleum hydrocarbons through migration of hydroxyl radicals by increasing soil polarity. Environmental Geochemistry and Health, 48(14), Article 586. https://doi.org/10.1007/s10653-026-03486-0

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03486-0

Keywords: petroleum hydrocarbons, Fenton oxidation, hydroxyl radicals, soil polarity, soil remediation, humic acid, FTIR, 3DEEM, advanced oxidation, contaminated soil, Efficient, direct

The research, published in Cleaner Engineering and Technology by a team from the Tecnológico Nacional de México led by Bethsabet Jaramillo-Sierra, tackles a contamination problem that spans the globe. Acetaminophen has been detected in wastewater and surface waters on nearly every continent, at concentrations ranging from tens of nanograms per liter in France and Canada to hundreds of micrograms per liter in Colombia and northern Mexico. Although each individual measurement may seem small, the compound’s sheer consumption volume, its availability over the counter, and its resistance to biological degradation mean it accumulates persistently in rivers, drinking water sources, and even treated effluents.

The concern is not merely the presence of the parent molecule. Acetaminophen is poorly biodegradable, so it passes through conventional treatment largely intact, and it has been linked in laboratory studies to genetic damage, oxidative lipid degradation, and liver injury in living organisms. Worse still, during some tertiary treatment steps the compound can transform into by-products that are more dangerous than the original drug, including 1,4-benzoquinone and N-acetyl-p-benzoquinone imine, a hepatotoxic metabolite capable of causing hepatic failure and necrosis. Any credible remediation strategy must therefore do more than hide the molecule; it must destroy it or convert it into harmless end products.

The Mexican team turned to advanced oxidation processes, or AOPs, a family of water treatment methods that operate at ambient temperature and pressure and rely on the generation of highly reactive chemical species, most notably the hydroxyl radical. This radical carries a higher oxidation potential than chlorine and reacts non-selectively with a broad range of organic pollutants, which makes it attractive for treating trace contaminants of many kinds. AOPs also avoid sludge production, do not require adsorbents that need controlled disposal, and can be driven by easily handled reagents such as ozone and hydrogen peroxide, with ozone generated on site from atmospheric air to reduce storage and transport costs.

The experimental apparatus was deliberately simple: a cylindrical stainless-steel reactor with an 11-watt ultraviolet lamp emitting at 200 to 280 nanometers, housed in a quartz tube, coupled to a 12-watt ozone generator and a recirculating reservoir. Synthetic solutions of acetaminophen at 100 milligrams per liter were treated for 60 minutes in 500-milliliter batches, with hydrogen peroxide added at doses of 5, 10, and 15 milligrams per liter. Degradation was tracked by ultraviolet-visible spectrophotometry, chemical oxygen demand was measured colorimetrically, and oxidation by-products were identified using gas chromatography-mass spectrometry following solid-phase extraction.

The results revealed a clear hierarchy of effectiveness. Ultraviolet light alone managed only about 11 percent degradation in an hour, primarily by photolyzing water molecules into hydroxyl radicals and hydrogen atoms, a process that accelerates around the 254-nanometer wavelength. Hydrogen peroxide alone reached roughly 27 percent at the highest dose. Ozone alone, attacking through both direct molecular oxidation and indirect decomposition into hydroxyl radicals, achieved 73 percent. Pairing ozone with ultraviolet light pushed the figure to 84 percent, because photolysis of dissolved ozone generates additional atomic oxygen, hydroxyl radicals, and even hydrogen peroxide in solution, creating multiple parallel destruction pathways.

The real breakthrough came when all three agents were applied simultaneously. The ozone-hydrogen peroxide combination, known as peroxone, promotes hydroxyl radical formation through the mutual reaction of the two oxidants, and adding ultraviolet irradiation on top of this triggered photolysis of both peroxide and dissolved ozone. Under these conditions, with an initial hydrogen peroxide concentration of just 5 milligrams per liter, the team achieved 99 percent acetaminophen degradation in 60 minutes. Notably, the study found an optimal peroxide dose: higher concentrations of 10 and 15 milligrams per liter actually performed worse over time, because excess peroxide and the hydroperoxyl radical it forms act as scavengers, consuming the very hydroxyl radicals that destroy the pollutant.

Chemical analysis confirmed that the combined treatment went beyond mere transformation. Carbon dioxide production rose steadily across the treatment combinations, peaking at 37 milligrams per liter for the triple system, evidence of genuine mineralization rather than simple conversion to other organics. Chemical oxygen demand removal reached 74 percent in the same configuration, compared with just 9 percent for ultraviolet light alone. Color measurements told a parallel story: untreated solutions stayed clear, ultraviolet treatment alone produced a pale carmine tint at 150 platinum-cobalt units as aromatic ring breakdown products accumulated, while the triple system yielded only a faint yellow at 5 units, indicating that even the colored intermediates were being further oxidized. Gas chromatography-mass spectrometry identified by-products dominated by carboxylic acid, ester, and alcohol structures arising from aromatic ring cleavage and recombination, and crucially, the team did not detect hydroquinone or 1,4-benzoquinone, suggesting these hazardous intermediates were themselves degraded during the process.

Energetically, the triple treatment also proved competitive. The researchers calculated the electrical energy per order, a standard metric describing the kilowatt-hours needed to reduce pollutant concentration by one order of magnitude per cubic meter, and obtained 23.00 kilowatt-hours per cubic meter for the peroxide-ozone-UV system, well below the 537 kilowatt-hours per cubic meter required for ultraviolet treatment alone and below several values reported in comparable literature. The estimated operating cost of the best configuration came to 5.04 US dollars per cubic meter, with ultraviolet irradiation dominating the energy bill, ozone generation second, and hydrogen peroxide contributing least. The degradation kinetics followed a pseudo first-order model, with rate constants rising as processes were combined, consistent with the theory that degradation depends primarily on pollutant concentration while oxidant doses remain effectively constant.

Finally, the team assessed whether the treated water was actually safer, using the germination of lettuce seeds as a biological toxicity screen. Untreated and lightly treated samples showed moderate toxicity, with ozone alone inhibiting germination by 40 percent, a sign that oxidative intermediates can be more harmful than the parent drug. But the full triple treatment reduced inhibition to 15 percent, close to the control level, demonstrating that synergistic oxidation both destroys the pollutant and neutralizes its residual toxic footprint. Taken together, the findings position the combined peroxide-ozone-UV process as an operationally simple, reproducible, and relatively inexpensive route to eliminating one of the world’s most ubiquitous pharmaceutical pollutants, though the authors note that complete mineralization would likely require longer treatment times or more intensified oxidative conditions to drive the remaining low-complexity organic by-products all the way to inorganic carbon.

Subject of Research: Degradation of the pharmaceutical pollutant acetaminophen in water using combined advanced oxidation processes involving ozone, hydrogen peroxide, and ultraviolet radiation.

Article Title: Acetaminophen degradation process applying a combination of oxidizing agents and ultraviolet radiation

Article References: Jaramillo-Sierra, B., Mercado-Cabrera, A., Ibañez-Olvera, M., Peña-Eguíluz, R., Rodríguez-Méndez, B. G., & López-Callejas, R. (2026). Acetaminophen degradation process applying a combination of oxidizing agents and ultraviolet radiation. Cleaner Engineering and Technology, 34, Article 101301. https://doi.org/10.1016/j.clet.2026.101301

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101301

Keywords: acetaminophen, paracetamol, advanced oxidation processes, ozone, hydrogen peroxide, ultraviolet radiation, hydroxyl radicals, wastewater treatment, pharmaceutical pollution, water purification, mineralization, chemical oxygen demand