Xiaojie Sun

Loading dissolved organic matter (DOM) onto iron–manganese oxides (FeMnOx) was a promising strategy for enhancing the hexavalent chromium (Cr(VI)) removal from wastewater. To optimize this process and gain deeper mechanistic insight, this study systematically investigated the DOM loading characteristics onto FeMnOx and its subsequent effect on Cr(VI) adsorption. DOM loading onto FeMnOx was significantly affected by the initial concentration of DOM and pH, with optimal loading conditions identified as a DOM concentration of 75 mg/L, pH of 4, ionic strength of 0.005 mol/L, temperature of 50 °C, and contact time of 4 h. During loading, FeMnOx preferentially adsorbed low-molecular-weight/low-aromaticity components such as tryptophan-like (C1) and fulvic acid-like (C2) substances. The adsorption process followed a non-uniform monolayer surface adsorption and involved multiple stages dominated by chemical interactions. DOM coating on FeMnOx significantly enhanced the Cr(VI) removal, and the maximum adsorption capacity under optimal loading conditions increased from 18.46 mg/g to 23.26 mg/g. Characterization by SEM-EDS, BET, ICP-MS, XPS, FTIR, and CV revealed that a moderate DOM loading (55–75 mg/L) enhanced the material’s surface reducibility and mesoporous structure. This improvement was attributed to the reduction of surface Mn(IV) to more-reactive Mn(III) by reductive functional groups in DOM, thereby promoting Cr(VI) adsorption and reduction. In contrast, excessive DOM loading (105 mg/L) formed a dense organic layer that masked active sites and hindered electron transfer, ultimately compromising the long-term reductive capability. These findings elucidate the concentration-dependent regulatory role of DOM in modifying FeMnOx properties, providing a theoretical foundation for the rational design of efficient DOM–metal oxide composites for heavy metal remediation in aquatic environments.

A novel Ag₃PO₄/BiVO₄ heterojunction was synthesized via a combined hydrothermal–in situ precipitation method. With an optimal Bi:Ag molar ratio of 1:2 and after calcination at 200 °C for 22 h, 0.9 g of this composite reduced the chemical oxygen demand (COD) of landfill leachate tailwater from 232 mg·L⁻¹ to 142 mg·L⁻¹ and its UV₂₅₄ absorbance from 0.22 to 0.156 under visible light irradiation within 140 min. The material exhibited a bandgap of 2.56 eV, along with enhanced visible-light absorption and improved charge-carrier separation efficiency. In the Ag₃PO₄/BiVO₄/peroxymonosulfate (PMS)/visible light system, using 0.5 g of catalyst and 2.0 g·L⁻¹ of PMS at pH 11 reduced the COD from 242 mg·L⁻¹ to 138 mg·L⁻¹. A subsequent two-stage treatment process, integrating the Ag₃PO₄/BiVO₄/PMS/vis and P25/UV process, achieved a final tailwater COD of 90 mg·L⁻¹—meeting standard discharge limits—and a 69.5% removal of humic-like substances. The heterojunction catalyst retained its activity over four consecutive cycles. Radical quenching experiments and electron paramagnetic resonance (EPR) spectroscopy identified photogenerated holes (h⁺), hydroxyl radicals(·OH), and sulfate radicals (SO₄⁻·) as the primary reactive species. Gas chromatography–mass spectrometry (GC–MS) analysis identified intermediate organic compounds and proposed plausible degradation pathways. These results support a reaction mechanism in which h⁺ oxidizes H₂O to generate ·OH, while PMS accepts electrons to produce SO₄⁻· and further ·OH radicals, leading to effective pollutant mineralization. Collectively, this solar-driven, sulfate radical-based advanced oxidation process offers an energy-efficient strategy with reduced chemical consumption for the sustainable treatment of refractory wastewater.

Humins (HMs), the insoluble faction of humic substances (HSs), play a pivotal role in the bioremediation of pollutants by acting as electron shuttles that modulate the interactions between microorganisms and pollutants. This crucial function is intricately linked to their structural composition and electron transfer capabilities. However, the dynamics of the electron transfer capacity (ETC) of HM extracted during the composting process and its determinants have yet to be fully elucidated. This study undertakes a comprehensive analysis of the ETC of HM derived from composting, employing electrochemical techniques alongside spectroscopic methods and elemental analysis to explore the influencing factors, including the electron accepting capacity (EAC), electron donating capacity (EDC), and electron reversible rate (ERR). Our findings reveal substantial variations in the EAC and EDC of HM throughout the composting process, with EAC values ranging from 133.03-220.98 mu mol e- gC-1 and EDC values from 111.17-229.33 mu mol e- gC-1. Notably, the composting process enhances the ERR and EDC of HM while diminishing their EAC. This shift is accompanied by an augmented presence of aromatic structures, polar functional groups, quinones, and nitrogen - and sulfur-containing moieties, thereby boosting the HM's EDC. Conversely, the reduction in EAC is associated with a decline in lignin carbon content and the abundance of oxygen-containing moieties, as well as the diminishment of visible fulvic-like and protein-like substances within HM. Importantly, humic-like substances and nitrogen-containing moieties within HM demonstrated the capacity for repeated electron transfer, underscoring their significance in the context of environmental remediation. GRAPHICAL ABSTRACT

Biochar has attracted attention for its capability to remove phosphorus (P) from wastewater. However, the poor dispersion and limited adsorption capacity of unmodified biochar prevent its wide usage in water remediation. Herein, sludge biochar was modified using lanthanum nitrate to improve the removal of P from aqueous solutions. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to elucidate the modification and adsorption mechanisms of biochar. Furthermore, the adsorption performance of the modified biochar was determined through adsorption kinetics and isotherm model fitting. The results showed that the modification process successfully introduced lanthanum-containing functional groups into biochar and considerably improved the complexation performance and ion-exchange capacity. The maximum experimental adsorption capacity for phosphate was 140.237 mg/g at pH 3.0. The adsorption processes of the modified biochar accorded with the Freundlich adsorption isotherm model, which indicates the successful adsorption of phosphate onto the modified biochar via multilayer adsorption. The adsorption mechanism was dominated by chemisorption, which mainly involved inner-sphere complexation, precipitation, and electrostatic attraction. Meanwhile, the adsorption and desorption experiments demonstrated the satisfying recycling performance of the modified biochar and the 72.3% adsorption capacity retention after the sixth desorption cycle. The dynamic adsorption study revealed that the modified biochar had long sustainable treatment durations of 7.58 and 9.08 h at adsorbent dosages of 1 and 2 g, respectively, which proves the feasibility of using biochar as a cost-effective and efficient adsorbent for phosphate-polluted water.

Using sewage sludge to produce biochar-based adsorbents to remove phosphate (P) from water can be a sustainable and cost-effective method of waste management. However, the adsorption efficiency of sewage sludge biochar is not high. In this study, lanthanum-modified sludge-based biochar (La-SBBC) was synthesized by combining lanthanum nitrate with dewatered sludge. La-SBBC exhibited the highest removal efficiency of 99.06% for an initial P concentration of 15 mg/L at pH 3.0 with a dosage of 1.3 g/L. The maximum adsorption capacity of La-SBBC for P was 152.77 mg/g at 35 °C. The adsorption process followed the pseudo-second-order kinetic model (R² ≥ 0.973) and the Freundlich isothermal adsorption model (R² ≥ 0.928). Multilayer chemisorption was identified as the controlling process. The primary mechanisms of P adsorption by La-SBBC involved electrostatic interactions, precipitation, and inner sphere complexation. Thermodynamic analysis revealed that the adsorption process of La-SBBC was a spontaneous endothermic reaction. The fixed-bed experiment demonstrated that La-SBBC had significant practical utility. La-SBBC maintained 76.6% of the original P removal efficiency after six cycles. Therefore, La-SBBC can be used as a promising adsorbent for P in practical applications.