The widespread industrial use of chromium has exacerbated water contamination issues globally. In this study, a nitrogen-doped wheat straw biochar loaded with nanoscale zero-valent iron composite (nZVI/N-KBC) was synthesized via a liquid-phase reduction method, and its adsorption properties for hexavalent chromium (Cr(VI)) in aqueous solutions were systematically investigated. The material was characterized using SEM, XRD, Raman spectroscopy, FTIR, and XPS. Experimental results demonstrated that under optimal conditions (pH 2, 0.05 g adsorbent dosage, and 50 mg/L initial Cr(VI) concentration), the adsorption capacity reached 41.29 mg/g. Isothermal adsorption analysis revealed that the process followed the Langmuir model, indicating monolayer adsorption with a maximum capacity of 100.9 mg/g. Kinetic studies show that the adsorption conforms to the pseudo-second-order kinetic model, and thermodynamic and XPS analyses jointly prove that chemical adsorption is dominant. Thermodynamic analyses confirmed the endothermic and entropy-driven nature of adsorption. Mechanistic studies via XPS and FTIR revealed a dual mechanism: (1) partial adsorption of Cr(VI) onto the nZVI/N-KBC surface, and (2) predominant reduction in Cr(VI) to Cr(III) mediated by Fe⁰ and Fe²⁺. This study highlights the synergistic role of nitrogen doping and nZVI loading in enhancing Cr(VI) removal, offering a promising approach for remediating chromium-contaminated water.

Advanced oxidation processes (AOPs) utilizing peroxymonosulfate (PMS) have emerged as a promising technology for organic pollutant degradation due to their distinct environmental advantages. In this study, copper–iron bimetallic oxide catalysts with varying ratios were synthesized via a co-precipitation method to activate PMS for degrading simulated tetracycline hydrochloride wastewater. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The effects of key parameters—including the PMS concentration, catalyst dosage, initial pH, and tetracycline hydrochloride concentration—on the degradation efficiency were systematically investigated. The results demonstrated that the CuFe(2)/PMS system exhibited the highest degradation efficiency. Under optimal conditions (20 mg/L tetracycline hydrochloride, 0.4 mM PMS, 0.5 g/L CuFe(2) catalyst, and pH 3), this system achieved a 94.12% degradation rate of tetracycline hydrochloride within 120 min. The electron paramagnetic resonance (EPR) tests and radical quenching experiments identified sulfate radicals (SO₄·⁻) as the predominant reactive species. Furthermore, the XPS analysis elucidated the persulfate activation mechanism, while the liquid chromatography–mass spectrometry (LC-MS) identified the potential degradation pathways and intermediate products of tetracycline hydrochloride.

The preparation of wheat straw biochar (MWSB) was optimized using response surface methodology (RSM) with a Box-Behnken Design (BBD) to maximize Cr(VI) removal. Parameters assessed were wheat straw particle size, KOH modifier concentration, and pyrolysis temperature. Optimal conditions (0.1 mm particle size, 3 mol/L KOH, 494 °C pyrolysis) yielded 86.5% Cr(VI) removal efficiency. Adsorption kinetics followed the pseudo-second-order model, and isotherm data fitted the Langmuir model, indicating monolayer adsorption limited by site density. The Langmuir model gave a maximum adsorption capacity (Qmax) of 105.28 mg/g at 25 °C. MWSB was characterized using SEM-EDS, FTIR, Raman spectroscopy, and XPS. The optimized MWSB preparation significantly enhanced the efficacy and feasibility of wheat straw in environmental applications, particularly for Cr(VI) removal.