The choice of ingredients is deliberate and each component plays a distinct structural role. Diatomite, a silica-rich sedimentary rock formed from the fossilized frustules of microscopic algae and sourced from Lampang in northern Thailand, supplies an intrinsically porous mineral framework that facilitates mass transfer of dye molecules into the pellet interior. Metakaolin, produced by calcining kaolin clay from Ranong, serves as the reactive aluminosilicate precursor that forms the chemically stable geopolymer network when activated with a mixture of sodium silicate solution and 10 M sodium hydroxide. Water hyacinth residue collected in Chiang Mai brings oxygen-rich functional groups and a fibrous morphology that modify the pore architecture and surface reactivity of the final composite. The researchers cast pastes containing 20 weight percent calcined diatomite, 15 weight percent metakaolin, and the alkaline activator, adding water hyacinth at 0, 1, 2, and 3 weight percent to produce a series labeled DG-WH0 through DG-WH3, which were then cured at room temperature for up to 28 days.

Structural analysis revealed how the biomass reshapes the material from the inside out. X-ray diffraction showed that quartz remained the dominant crystalline phase in all compositions, inherited largely from unreacted portions of the diatomite and metakaolin precursors, while a broad diffuse feature between roughly 20 and 35 degrees two-theta confirmed the presence of a poorly ordered aluminosilicate geopolymer matrix. Fourier-transform infrared spectroscopy identified the characteristic Si-O-T asymmetric stretching band near 1016 to 1021 per centimeter, along with hydroxyl and carbonate features, and small shifts in these bands after dye exposure hinted at interactions between methylene blue and the composite surface. Scanning electron microscopy told a more visually striking story: the biomass-free pellet was relatively dense, but increasing water hyacinth content progressively introduced interfacial gaps, larger voids, and interconnected pore channels, particularly in the 2 and 3 percent formulations.

Quantitative measurements reinforced what the micrographs suggested. Apparent porosity rose from 58.57 to 62.03 percent across the series, while water absorption climbed sharply from 58.30 to 79.55 percent, and bulk density fell from 1.22 to about 1.08 grams per cubic centimeter. Nitrogen physisorption on the two endpoint compositions showed that the BET specific surface area of the 3 percent pellet reached 14.843 square meters per gram, roughly 86 percent higher than the 7.986 square meters per gram of the biomass-free control, while total pore volume increased by about 75 percent. In other words, the invasive weed was effectively blowing open the internal architecture of the pellet, creating more pathways and more exposed surface for dye molecules to reach.

Surface charge added a second, electrostatic dimension to the story. Zeta potential measurements at pH 7 showed that all pellets carried negative surface charges, becoming progressively more negative as water hyacinth content increased, from minus 67.3 millivolts for the control to minus 74.9 millivolts for the highest-biomass pellet. The point of zero charge of the best-performing composition was approximately 2.22, meaning that at the pH used in the adsorption experiments the surface was decisively negative and therefore electrostatically attractive to positively charged methylene blue cations. Deprotonated surface hydroxyl groups on the aluminosilicate framework, generating negatively charged siloxide and aluminate sites, are thought to contribute to this favorable electrostatic environment.

The adsorption experiments bore out the design logic. At pH 2, performance was poor, with removal efficiencies between roughly 49 and 54 percent, because the flood of hydrogen ions competed with dye cations for adsorption sites. Performance peaked at pH 4, where the 3 percent pellet removed 77.25 percent of methylene blue with an equilibrium capacity of 19.31 milligrams per gram, and remained high but essentially flat from pH 6 through 10, indicating that electrostatics alone do not govern the process. Kinetic measurements showed rapid initial uptake followed by a gradual plateau between about 800 and 1080 minutes, with 24-hour removal reaching 77.03 percent and a capacity of 19.26 milligrams per gram for the best pellet. Increasing the initial dye concentration from 50 to 250 milligrams per liter lowered the removal percentage from 95.26 to 77.40 percent while raising the per-gram capacity from about 4.76 to 19.35 milligrams per gram, the classic signature of a fixed number of sites being progressively saturated.

Equilibrium data fit the Langmuir isotherm model better than the Freundlich model, with a linearized correlation coefficient of 0.9998 and a maximum monolayer capacity of 22.32 milligrams per gram, while both linearized and nonlinear kinetic analyses consistently favored the pseudo-second-order model. Against the backdrop of published geopolymer adsorbents, the 22.32 milligrams per gram figure is competitive, outperforming lightweight geopolymer-expanded glass composites, metakaolin/slag geopolymers, red mud and rice husk ash systems, and coal gangue-based materials, and landing close to reduced graphene oxide/geopolymer composites, though some fly ash and metakaolin systems report higher capacities. The authors caution that direct comparisons across studies are complicated by differences in material form and experimental conditions, and their pellets carry an inherent mass-transfer penalty because dye molecules must diffuse through the pellet interior rather than contacting a loose powder directly.

That penalty is the price of practicality, and the study is unusually candid about the trade-offs involved. Compressive strength after 28 days of curing fell from 21.5 megapascals for the biomass-free pellet to 9.1, 6.5, and 5.5 megapascals at 1, 2, and 3 percent water hyacinth, because the fibrous additive and its interfacial discontinuities disrupt the continuity of the load-bearing geopolymer matrix. The modest gain in equilibrium capacity at the highest biomass loading does not fully compensate for the substantial loss of mechanical robustness, so the researchers suggest that an intermediate water hyacinth content may offer the best balance for applications where pellets must survive handling. Reusability testing over five adsorption-desorption cycles showed another honest limitation: removal efficiency declined to about 33 percent of its initial value by the fifth cycle, even though the pellets retained roughly 99 percent of their mass, pointing to a need for improved regeneration protocols.

What makes this work resonate beyond its numbers is the circular economy story it tells. Water hyacinth is a global nuisance, clogging waterways, blocking navigation, and starving aquatic ecosystems of light and oxygen, yet here its residue becomes a functional ingredient in a low-cost ceramic adsorbent built from abundant local minerals. The study also models a kind of scientific honesty that is increasingly valued in materials research: rather than claiming a single dominant mechanism, the authors attribute dye uptake to coupled effects, including electrostatic attraction to the negatively charged surface, possible hydrogen bonding through hydroxyl-containing groups, and improved pore accessibility, while explicitly declining to claim mechanisms, such as pi-pi interactions, that their characterization could not verify. They note that methylene blue served only as a model cationic dye, and that real textile wastewater, with its mixtures of dyes, salts, and organic matter, will pose stiffer competitive challenges. Future work on mixed-pollutant systems, thermodynamic analysis, and regeneration chemistry will determine whether these weed-powered pellets can graduate from elegant laboratory concept to working technology for the dye-polluted rivers that need them most.

Subject of Research: Pelletized diatomite-based geopolymer composites incorporating water hyacinth biomass for the adsorptive removal of methylene blue dye from wastewater

Article Title: Pelletized diatomite-based geopolymer-water hyacinth composites for methylene blue adsorption: insights into structure-property-performance relationships

Article References: Thammarong, S., Zhang, W., Pimpha, N., Saenkam, K., Boontakam, W., Tandorn, S., Randorn, C., Srichumpong, T., Pengpat, K., & Rujijanagul, G. (2026). Pelletized diatomite-based geopolymer-water hyacinth composites for methylene blue adsorption: insights into structure-property-performance relationships. Results in Chemistry, 31, Article 103923. https://doi.org/10.1016/j.rechem.2026.103923

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103923

Keywords: geopolymer, water hyacinth, diatomite, methylene blue, adsorption, wastewater treatment, dye removal, metakaolin, porous materials, biomass composites, isotherm modeling, mechanical strength

The research, led by Pat Sooksaen and colleagues at Silpakorn University, addresses a stubborn gap in water treatment technology. Activated carbon remains the workhorse adsorbent for removing organic contaminants from industrial effluents, prized for its enormous surface area and broad affinity for organic molecules. Yet its high cost of production and, crucially, its expensive regeneration have kept many industries from adopting adsorption-based treatment at scale, particularly for high-volume, low-value waste streams such as metalworking coolant. Meanwhile, a vast literature on cheap natural adsorbents, from agricultural biochars to modified clays, has largely remained confined to powdered materials tested under idealized conditions with synthetic dye solutions, rarely confronting the granulation, mechanical strength and thermal processing demands of real industrial deployment.

The Thai team’s approach was deliberately simple. They combined two silica-rich precursors, rice husk ash supplied by a working rice mill in Nakhon Pathom and diatomite from a Bangkok supplier, with ordinary terracotta clay acting as a binder. Rice husk ash is the residue of combustion at 500 to 600 degrees Celsius, and it consists of fine, irregular grains riddled with nanoscale mesopores. Diatomite, by contrast, is composed of the fossilized cell walls of aquatic diatoms, preserving an intricate honeycomb architecture with pores generally smaller than five micrometres. X-ray fluorescence confirmed the raw materials’ credentials: the ash contained 84.37 weight percent silica and the diatomite 90.13 percent, while the terracotta contributed alumina and, importantly, iron oxide, which acts as a flux during firing.

Four formulations were prepared by ball milling, mixing either silica source with terracotta at volume ratios of 60:40 and 80:20, then shaping the blends into spherical granules using an in-house granulator rotating at 50 to 100 revolutions per minute with water as the binding agent. The granules were sieved to a narrow fraction of 5 to 9 millimetres, a size chosen for practical handling and separation rather than optimized kinetics, and then fired for one hour at 800, 1000 or 1200 degrees Celsius. This firing step proved to be the decisive variable in the entire study, governing whether the granules emerged as open, adsorbent-rich sponges or as dense, glassy pebbles with little capacity to hold contaminants.

The characterization data told a striking and somewhat counterintuitive story about the two silica sources. In its raw state, rice husk ash boasted a specific surface area of 33.45 square metres per gram, roughly twenty times that of raw diatomite, reflecting its finely mesoporous amorphous structure. But firing at just 800 degrees Celsius collapsed that area by more than 90 percent, to 2.66 square metres per gram, revealing that the ash’s delicate pore network is thermally metastable and begins to sinter well below the temperatures used in ceramic processing. Diatomite behaved in the opposite manner: heating to 800 degrees actually increased its surface area by about 47 percent and its pore volume by 56 percent, apparently because the burnout of residual organic matter and moisture unblocked channels in the diatom cell walls that had been obstructed in the raw rock.

X-ray diffraction explained the mechanism behind this degradation. Both raw materials were dominated by cristobalite, a crystalline form of silica, with alpha-quartz as a secondary phase. As firing temperature climbed from 800 to 1200 degrees, the cristobalite reflections grew sharper and more intense, marking the devitrification of the amorphous silica fraction into a thermodynamically ordered crystal lattice. This recrystallization goes hand in hand with pore collapse. Scanning electron micrographs showed that at 1000 to 1200 degrees, liquid-phase sintering driven by the iron oxide and alkali fluxes contributed by the terracotta fused particles together, eliminated open pores and produced smooth, dense surfaces that would severely restrict the diffusion of dye molecules into the granule interior. The characteristic cylindrical frustules of the diatomite partially collapsed as well.

The adsorption tests bore out these microstructural observations with almost brutal clarity. When 100 grams of granules were immersed in 200 millilitres of a 25 milligram-per-litre methylene blue solution, a standard cationic dye used to benchmark adsorbents, and aerated for four hours at room temperature, the granules fired at 800 degrees performed dramatically best. The 60RHA:40T formulation removed 97.7 percent of the dye, corresponding to an uptake of 0.0487 milligrams per gram under these screening conditions, while the diatomite-based 80D:20T granules achieved 93.0 percent. At 1000 degrees, removal fell to between 51.6 and 86.8 percent, and at 1200 degrees it collapsed to as little as zero for the 60D:40T formulation, a direct mirror of the pore closure documented by electron microscopy and porosimetry.

Infrared spectroscopy provided a molecular-level view of how the dye binds. Before adsorption, the granules displayed the signature of a silanol-terminated silica surface: a broad hydroxyl stretching band near 3450 wavenumbers, strong silicon-oxygen-silicon stretching modes between 1140 and 1080 wavenumbers, and bending modes near 800 and 460 wavenumbers. After dye uptake, two new features appeared, an aromatic ring-stretching band near 1600 wavenumbers and a carbon-sulfur-carbon stretch at 615 to 625 wavenumbers, both characteristic of methylene blue. Their appearance alongside the silica framework bands supports electrostatic binding of the cationic dye to deprotonated silanol sites on the ceramic surface, although the authors are careful to note that surface charge and pH effects were not established in this study.

Perhaps the most industrially significant result concerned reuse. Granules saturated with dye were heated in air at 600 degrees Celsius for one hour, decomposing the organic dye trapped within their pores. Infrared analysis showed the dye-associated bands almost completely vanished, with only a weak residual aromatic feature remaining in one formulation. When the regenerated granules were tested again, removal efficiencies of 85.4 to 93.8 percent were retained, only modestly below the original performance. This one-step thermal regeneration, achievable at temperatures far lower than those needed to reactivate spent activated carbon, is precisely the kind of economics-friendly feature that could make ceramic adsorbents competitive, although the authors emphasize that multi-cycle durability, mechanical attrition and long-term capacity retention remain untested.

Finally, the team selected the 80RHA:20T formulation, chosen for its higher proportion of cheap agricultural waste and lower binder demand rather than its top laboratory performance, for a qualitative demonstration at an aluminum ingot casting facility. Granules fired in a gas-fired refractory kiln at 900 to 1100 degrees were loaded into a 20-cubic-metre batch tank at an adsorbent-to-wastewater ratio of 1:5 and used to treat metalworking coolant effluent over a 30-hour cycle. The authors are candid that no quantitative influent and effluent analyses or activated-carbon baseline were obtained, so the trial demonstrates deployment feasibility rather than validated treatment performance. Even so, the study charts a credible path from rice mill waste to industrial water remediation, and points toward the analytical work, isotherms, pH studies, mechanical testing and repeated reuse trials, that will determine whether these humble ceramic granules can genuinely challenge activated carbon in the factories that need them most.

Subject of Research: Valorization of rice husk ash and diatomite into porous silica ceramic adsorbents for wastewater treatment

Article Title: Valorization of rice husk ash and diatomite into porous silica ceramics for industrial wastewater remediation: from dye adsorption to coolant treatment

Article References: Sooksaen, P., Thongyoug, P., Thipsupanimit, W., Sreearunothai, P., & Puathawee, P. (2026). Valorization of rice husk ash and diatomite into porous silica ceramics for industrial wastewater remediation: from dye adsorption to coolant treatment. Results in Chemistry, 31, Article 103921. https://doi.org/10.1016/j.rechem.2026.103921

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103921

Keywords: rice husk ash, diatomite, porous ceramics, silica, wastewater treatment, methylene blue, adsorption, coolant wastewater, terracotta, sintering, regeneration, industrial waste valorization

The study, published in Food Chemistry: X, explores what happens when low-density polyethylene (LDPE), the soft, flexible plastic commonly used for produce bags, is blended with raw diatomite, alkaline-activated diatomite, potassium permanganate, and potassium permanganate impregnated into activated diatomite. Diatomite, also known as diatomaceous earth, is an amorphous silica material formed from the fossilized cell walls of microscopic aquatic algae. It is remarkably porous, with voids making up roughly 80 to 90 percent of its volume, chemically inert, and inexpensive, which makes it attractive as a low-cost adsorbent. Its surface carries silicon hydroxyl groups that can attract organic molecules such as ethylene, but in its natural state the density of these groups is often too low to be highly effective.

To unlock diatomite’s full adsorption potential, the researchers activated it with a strong alkaline treatment. Purified diatomite powder was milled through a 200-mesh sieve, washed, and then immersed in 5 molar sodium hydroxide solution at 85 degrees Celsius for one hour. This harsh chemical bath dissolves impurities that clog the mineral’s natural pores and induces partial dissolution and rearrangement of its structural ions, increasing the specific surface area and optimizing the distribution of surface functional groups. The activated material was then impregnated with potassium permanganate by soaking it in a 2 normal KMnO4 solution at low temperature, yielding particles with a manganese oxide content of roughly 18.5 percent and a permanganate uptake of about 2.82 grams per 100 grams of diatomite, a loading comparable to commercial ethylene-scavenging sachets.

The treated and untreated particles were then compounded into LDPE using industrial melt processing. The team first prepared 10 percent masterbatches in a twin-screw extruder and then diluted them into blown films containing 1, 3, and 5 weight percent of each filler, producing films 30 to 40 micrometers thick. This manufacturing route matters because it uses the same equipment that produces commercial packaging, meaning the concept could, in principle, be scaled without exotic new machinery. Spectroscopic analysis confirmed that the polymer matrix remained chemically intact and that the permanganate was retained in an active form within the films, while thermal analysis showed that diatomite slightly raised the onset of thermal degradation from 447 to about 459 degrees Celsius, thanks to the mineral’s insulating character.

The ethylene removal results revealed a striking and somewhat counterintuitive pattern. In powder form, the alkaline-activated, permanganate-impregnated diatomite was the star performer, removing about 909 microliters of ethylene per gram within 24 hours, far outpacing neat potassium permanganate powder, whose limited gas-accessible surface and tendency to agglomerate hampered its performance. Once embedded in LDPE films, however, the picture changed. The best-performing films were those containing just 1 weight percent of the impregnated particles, which removed 373 microliters of ethylene per gram over 48 hours, and 1 weight percent of plain diatomite, which removed 297 microliters per gram. Surprisingly, raising the loading to 3 or 5 percent actually reduced ethylene removal. Scanning electron microscopy explained why: at higher loadings, the polar mineral particles clump into large agglomerates within the non-polar polymer, burying active sites and blocking gas transport, while at 1 percent the particles disperse relatively uniformly.

The study also delivered a sobering lesson about gas barriers. Contrary to what has been reported for some other mineral-polymer systems, adding diatomite did not improve the films’ resistance to gas diffusion. The oxygen transmission rate of the 1 percent diatomite film actually increased by about 132 percent compared with neat LDPE, and water vapor transmission rose slightly as well. The researchers attribute this to a fundamental mismatch: hydrophilic diatomite, covered in silanol groups, bonds poorly with hydrophobic polyethylene, creating microscopic voids at the interface through which gases pass more easily. Mechanical properties told a similar story, with tensile strength and elongation declining as filler content increased, although films with 1 percent alkaline-activated diatomite retained strength values between 15 and 19 megapascals, comparable to commercial LDPE films used for fresh produce. Optical clarity, meanwhile, was essentially preserved at 1 percent loading, an important consideration for shoppers who want to see the fruit they are buying.

The decisive test came with real bananas. Mature green bananas harvested in Ratchaburi Province, Thailand, were packed individually in bags made from neat LDPE, 1 percent diatomite LDPE, or 1 percent permanganate-impregnated activated diatomite LDPE, then stored for 10 days at 25 degrees Celsius alongside an unpacked control group. The results were dramatic. Unpacked bananas lost nearly 18 percent of their weight and developed dark spots and dried peel by day 6, while all packaged fruits stayed within 2 to 3 percent weight loss. But the packaging types diverged sharply in how well they slowed ripening itself. Bananas in the 1 percent diatomite film kept their green peel through the entire 10-day storage period, showed only a slight decline in firmness, and reached a total soluble solids level of just 6.97 degrees Brix by day 10, compared with 16.63 degrees Brix for bananas in plain LDPE and 9.80 degrees Brix for the unpacked control.

Perhaps the most intriguing finding is that the film with the highest measured ethylene removal was not the best at preserving the fruit. The permanganate-impregnated film removed more ethylene in closed-vial tests, yet the plain diatomite film delivered superior banana quality. The authors suggest that postharvest performance is governed not by ethylene scavenging alone but by the balance among ethylene removal, gas permeability, and moisture regulation. The higher oxygen transmission of the diatomite film may have helped maintain healthy aerobic respiration, while its higher water vapor permeability prevented condensation on the fruit surface, avoiding the peel softening and lenticel damage associated with saturated humidity. The researchers are careful to note that their closed-vial measurements do not directly represent the dynamic atmosphere inside a package containing respiring fruit, and that simultaneous monitoring of ethylene, oxygen, and carbon dioxide in actual packages will be needed to disentangle these effects.

The team is equally candid about the limits of the work. The films remain a laboratory-scale proof of concept: long-term stability of the polymer matrix, potential migration of permanganate or manganese into food, and overall food-contact safety were not evaluated, so the materials cannot yet be considered suitable for direct commercial use. Still, the study opens a genuinely novel direction. Diatomite had never before been investigated as an ethylene adsorbent embedded in a polymer matrix for fruit packaging, and the finding that a simple, cheap, unmodified mineral at just 1 percent loading can outperform more elaborate chemically treated formulations is the kind of result that could reshape how the packaging industry thinks about active films. If subsequent safety and scale-up studies succeed, the fossilized shells of ancient algae, one of nature’s most abundant porous materials, could soon be quietly working inside the plastic bags at the grocery store, buying bananas and other climacteric fruits an extra week of freshness and keeping a little more of the global harvest out of the bin.

Subject of Research: Ethylene-scavenging LDPE composite films with diatomite and potassium permanganate for extending banana shelf life

Article Title: Effect of diatomite and KMnO 4 -impregnated diatomite in LDPE films on ethylene removal and postharvest quality of bananas

Article References: Yann, T., Winotapun, C., Yos, P., Voon, L. H., Wong, Y. H., Ngamchuachit, P., & Boondamnoen, O. (2026). Effect of diatomite and KMnO4-impregnated diatomite in LDPE films on ethylene removal and postharvest quality of bananas. Food Chemistry: X, 39, Article 104499. https://doi.org/10.1016/j.fochx.2026.104499

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104499

Keywords: ethylene scavenger, diatomite, potassium permanganate, LDPE film, active packaging, banana shelf life, postharvest quality, food packaging, blown film extrusion, climacteric fruit, alkaline activation, Food Chemistry: X