Degradation of humic acid by UV/PMS: process comparison, influencing factors, and degradation mechanism.

In natural water bodies, humic acid (HA), generated during the chlorination disinfection process at water treatment plants, can produce halogenated disinfection by-products, increasing the risk to drinking water safety and posing a threat to human health. Effectively removing HA from natural waters is a critical focus of environmental research. This study established a synergistic ultraviolet/peroxymonosulfate (UV/PMS) system to remove HA from water. It compared the efficacy of various UV/advanced oxidation processes (AOPs) on HA degradation, and assessed the influence of different water sources, initial pH, oxidant concentration, and anions (HCO3 -, Cl-, NO3 -) on HA degradation. The degradation mechanism of HA by the UV/PMS process was also investigated. Results showed that under the conditions of 3 mmol L-1 PMS concentration, 10 mg L-1 HA concentration, initial solution pH of 7, and a reaction time of 240 minutes, the mineralization rate of HA by UV/PMS reached 94.15%. The pseudo-first-order kinetic constant (k obs) was 0.01034 and the single-electric energy (EE/O) was 0.0157 kW h m-3, indicating superior HA removal efficiency compared to other systems. Common anions (HCO3 -, Cl-, NO3 -) in water were found to inhibit the degradation of HA, and acidic conditions were more conducive to HA removal, with the optimal pH being 3. Free radical quenching experiments showed that both sulfate radical (SO4 -˙) and hydroxyl radical (˙OH) radicals were involved in HA degradation, with SO4 -˙ being the primary oxidant and ˙OH as the auxiliary species. Analyses using 3D-excitation-emission matrix (EEM), parallel factor analysis (PARAFAC), specific fluorescence index, and absorbance demonstrated that UV/PMS technology could effectively degrade HA in water. This study provides theoretical references for further research on the removal of HA and other organic substances using UV/PMS technology.

Reproducible 2D Ti3C2T x for perovskite-based photovoltaic device.

Ti3C2T x (T x denotes terminal group), resulting from two-dimensional (2D) Mxenes, has attracted significant attention due to energy shortage and catalysis. Herein, we present reproducible 2D Ti3C2T x obtained from commercial bulk Ti3AlC2 using a cost-effective and environment-friendly approach. Both etching and exfoliation processes were investigated with the rational selection of etchant, reaction time and exfoliation solution. The hydrofluoric acid (HF) etchant plays a key role in the production of 2D Ti3C2T x and therefore the recycling of HF is addressed for reproducible 2D MXenes. Hazardous HF waste was also neutralized via CaF2 precipitation according to the regulations for HF sewage. Equally important, dimethyl sulfoxide (DMSO) was employed to promote the exfoliation of multilayer Ti3C2T x MXenes into Ti3C2T x nanosheets in an aqueous solution, which can couple with terminal groups and protect the exfoliated single-layers from recombination, facilitating interface passivation toward perovskite solar devices. The resulting perovskite solar cell exhibited striking improvements to achieve champion efficiency, with a PCE of 19.11%, which accounts for ∼9% enhancement as compared to pristine devices.