In the quest to tackle the persistent challenge of fulvic acid (FA) contamination in water systems, breakthroughs are arising from the intersection of advanced materials science and environmental chemistry. FA, a complex component of humic substances, presents considerable resistance to degradation due to its intricate aromatic architecture and diverse oxygen-containing functional groups. These properties confer exceptional chemical stability that limits the efficacy of conventional photocatalytic approaches. While photocatalysis under light irradiation capable of generating reactive oxygen species (ROS) has been studied extensively, its utility remains hampered by the limited absorption of visible light and rapid recombination of photogenerated charge carriers, factors that curtail the overall efficiency of pollutant degradation.
FA emerges from the transformation of organic matter in soils and surface waters, comprising macromolecules laden with aromatic rings, carboxyl groups, and phenolic hydroxyls. These functionalities have a strong affinity for metals and co-existing contaminants, which modulates their environmental fate by affecting bioavailability and mobility. In drinking water treatment, the presence of FA is problematic, as its interaction during chlorination leads to the formation of hazardous disinfection by-products (DBPs) such as trihalomethanes and haloacetic acids, substances known for their adverse health implications. Thus, developing robust strategies for FA removal prior to chlorination is critical to safeguarding public health and ensuring water purification efficacy.
Addressing these challenges, a pioneering study conducted by Guangshan Zhang and Chunyan Yang’s research team at Qingdao Agricultural University offers an innovative photocatalytic system that synergistically enhances the degradation of FA. Published in the journal Agricultural Ecology and Environment, this investigation leverages a BiOCl/MXene composite photocatalyst integrated with peroxymonosulfate (PMS) to substantially boost radical generation under visible-light irradiation, thereby accelerating the breakdown of FA in water matrices. The research provides detailed mechanistic insights and establishes optimized operating conditions to maximize catalytic performance.
The research team employed a comprehensive suite of characterization techniques to unravel the physicochemical properties and catalytic potential of the BiOCl/MXene composite. Scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) mapping revealed homogeneous anchoring of BiOCl nanosheets on layered MXene substrates, enabling intimate interfacial contact critical for efficient electron transfer. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) provided crystallographic evidence of exposed BiOCl (101) and (110) facets alongside MXene (002) planes, underscoring the structural stability of the heterojunction. X-ray diffraction (XRD) patterns confirmed the phase coexistence without unwanted phase impurities, ensuring an active composite structure.
Surface area and porosity, pivotal elements influencing catalytic activity, were assessed through nitrogen adsorption–desorption isotherms employing BET analysis. The BiOCl/MXene composite displayed a marked increase in mesoporous surface area reaching 41.73 m²/g compared to pristine BiOCl’s 9.17 m²/g, indicating enhanced exposure of active sites and improved mass transfer capabilities. X-ray photoelectron spectroscopy (XPS) revealed shifts in binding energies alongside the formation of Bi–O–C bonds, signaling effective electron transfer pathways and establishment of Schottky junctions at the BiOCl/MXene interface, pivotal for the separation of photoinduced charge carriers and reduction of recombination losses.
Central to the catalytic performance is the activation of PMS by the BiOCl/MXene composite under visible-light irradiation. Experimentation revealed that optimized synthesis conditions—specifically, a hydrothermal temperature of 160 °C for 10 hours with a 15% MXene loading—resulted in approximately 98.43% FA degradation within 30 minutes. The apparent rate constant was calculated at 0.1388 min⁻¹, representing a 3.27-fold enhancement over bare BiOCl, while the synergy factor was estimated at 5.28. Measured apparent quantum yield reached about 1.33%, indicating efficient photon utilization facilitated by PMS-mediated electron trapping mechanisms.
Versatility and robustness of the catalytic system were emphasized by its consistent performance across a broad pH spectrum ranging from 3 to 9 and varying FA concentrations between 20 and 100 mg/L. The catalyst loading optimized at 0.8 g/L accompanied by approximately 2 mM PMS offered ideal conditions for maximal degradation efficiency. Importantly, durability testing demonstrated that catalytic activity remained above 80% even after five decomposition cycles. Additionally, real water matrices such as lake water and a variety of organic pollutants, including antibiotics, dyes, and phenolic compounds, were effectively degraded, highlighting the composite’s potential for practical environmental remediation applications.
The research incorporated an array of photoelectrochemical techniques to elucidate the underlying electron dynamics and reactive species involved in the degradation process. Ultraviolet-visible spectroscopy (UV–vis) and photoluminescence (PL) studies confirmed an expanded visible-light absorption profile and suppressed PL intensity, indicative of reduced charge recombination. Electrochemical impedance spectroscopy (EIS) and transient photocurrent responses demonstrated accelerated interfacial charge transfer, while Mott–Schottky analysis affirmed suitable band structure alignment for effective photocatalysis. Radical quenching tests along with electron paramagnetic resonance (EPR) spectroscopy identified holes (h⁺) and superoxide radicals (O₂•⁻) as dominant reactive oxidants in the removal of fulvic acid.
Complementing radical identification, detailed spectroscopic analyses including specific ultraviolet absorbance (SUVA) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy probed molecular-level transformations within FA. The findings indicated rapid degradation of aromatic chromophores, although total organic carbon (TOC) analysis revealed partial mineralization, with roughly 49.95% conversion to inorganic carbon. This suggests successive progressive breakdown stages leading towards complete mineralization with extended treatment duration or optimizations.
The significance of this research transcends academic interest, addressing a pressing environmental and public health concern related to the formation of toxic disinfection by-products in drinking water. By providing a recyclable, visible-light-active photocatalyst capable of activating PMS efficiently, this system withstands challenges posed by fluctuating pH and complex aqueous environments, marking an advance toward viable water treatment technologies. Furthermore, its broad-spectrum efficacy against diverse pollutant classes reflects adaptability as an advanced oxidation process (AOP) platform, potentially revolutionizing treatment frameworks for waters contaminated by complex mixtures.
By merging advanced catalytic design with mechanistic clarity, the BiOCl/MXene/PMS system crafted by Zhang and Yang’s team offers a transformative solution to persistent humic substance pollution. This integration of layered MXene materials with bismuth oxychloride under visible light represents a promising paradigm, leveraging synergistic effects to overcome traditional photocatalytic limitations. Future research expanding on this platform could extend to pilot-scale demonstrations and explore integration with existing infrastructure, ultimately contributing to safer, cleaner water supplies worldwide.
Subject of Research: Not applicable
Article Title: Synergistic photocatalysis of BiOCl/MXene activates peroxymonosulfate for enhanced fulvic acid degradation: performance and mechanism insights
News Publication Date: 20-Jan-2026
References:
DOI: 10.48130/aee-0025-0014
Keywords:
Photocatalysis, Fulvic Acid, BiOCl/MXene Composite, Peroxymonosulfate Activation, Visible-Light Catalysis, Water Treatment, Reactive Oxygen Species, Charge Carrier Separation, Humic Substances, Disinfection By-products, Environmental Remediation
