Environmental-friendly hydrochar-montmorillonite composite for efficient catalytic degradation of dicamba and alleviating its damage to crops

Layered clay confined single-atom catalyst for enhanced radical pathway to achieve ultrafast degradation of bisphenol A

Seeking a technically promising method and cost-effective material to synthesize carrier-supported single-atom catalysts has attracted on-going research interests to overcome the low productivity and high costs for their industrial application. Montmorillonite (MT), a natural silicate clay mineral, has specific two-dimensional layered structure, and could be an excellent carrier, which creates a unique microenvironment to enhance molecule adsorption and interfacial reactions within the single atoms, free radicals and pollutants in the heterogeneous catalytic system. We synthesized cobalt single-atom catalyst (Co-SAC) by ball milling MT and cobalt salt using surface and spatial confinement strategy. Co-SAC/MT catalyst was used to activate peroxymonosulfate for degrading emerging contaminants bisphenol A (BPA). Characterization results revealed that Co single atoms were confined in the interlayer of MT as Co-O6-Si. Co-SAC/MT catalyst demonstrated remarkable molecular interaction capabilities to shorten mass transfer distance of free radical diffusion to the target pollutants, enhance the utilization rate of free radicals, and thus improve the efficiency of oxidation reaction. The BPA solution was completely degraded in 3 min, with a mineralization rate of 75.7 % in 10 min. This study provides a simple and efficient method for the preparation of single-atom catalysts, which is expected to achieve large-scale production of single-atom catalysts.

Degradation of dicamba - A persistent herbicide - By combined application of formic acid and UV as an advanced reduction process

The degradation of dicamba as a persistent herbicide was studied with the combined application of UV and formic acid (FA) as a novel advanced reduction process (ARP). The effects of key parameters of FA concentration, dissolved organic matter, and inorganic anions were studied. A 97 % degradation and 94 % dechlorination of dicamba were obtained through the combination of UV and FA (UV-FA) at a dicamba concentration of 0.023 mM and FA concentration of 0.123 M. With respect to the dechlorination, at a dicamba concentration of 0.23 mM, FA concentration of 0.123 M, and pH of 2, chloride concentration of 12.4 mg/L and 5.2 mg/L was obtained for ARP (UV-FA) and sole UV in acidic condition, respectively. Scavenging test using Methyl viologen (MV2 +) as a scavenger for reductive radicals including carboxyl anion radicals (CO2•¯) led to a decrease in the chloride concentration to 1.7 mg/L, revealing the importance of this radical in the dechlorination of dicamba. Inorganic anions (CO32¯ and SO42¯) had a slightly positive effect on the degradation of dicamba and led to an increase in degradation to 99 %, while they had a negative effect on the dechlorination by 7 % and 30 %, respectively. Due to the turbidity induced by dissolved organic matters (DOM), a moderate decrease in degradation by 39 % and dechlorination by 30 % was observed. The existence of five intermediates identified by GC-MS technique confirmed the proposed mechanism of dicamba degradation via ARP. Reductive degradation of dicamba mainly consists of processes based on CO2•¯, including single electron transfer process and radical-nucleophilic aromatic substitution (SRN) reactions, demonstrating the capability of this ARP for the effective degradation of dicamba.

Insights into the efficient water treatment over N-doped carbon nanosheets with layered minerals as template: The role of interfacial electron tunneling and transfer

Peroxymonosulfate (PMS) oxidation reactions have been extensively studied recently. Due to the high material cost and low catalytic capability, PMS oxidation technology cannot be effectively applied in an industrial water treatment process. In this work, we developed a modification strategy based on enhancing the neglected electron tunneling effect to optimize the intrinsic electron transport process of the catalyst. The 2D nitrogen-doped carbon-based nanosheets with small interlayer spacing were prepared by self-polymerization of dopamine hydrochloride inserted into the natural layered bentonite template. Systematic characterizations confirmed that the smaller layer spacing in the 2D nitride-doped carbon-based nanosheets reduces the depletion layer width. The weak electronic shielding effect derived by the small layer spacing on the material subsurface enhanced the bulk electron tunneling effect. More bulk electrons could be migrated to the catalyst surface to activate PMS molecules. The PMS activation system showed ultrafast oxidation capability to degrade organic pollutants and strong ability to resist interference from environmental matrixes due to the optimized electron transfer process. Furthermore, the developed membrane reactor exhibited strong catalytic stability during the continuous degradation of P-Chlorophenol (CP).

Sulfur Vacancy-Engineered Co3S4/MoS2-Interfaced Nanosheet Array for Enhanced Alkaline Overall Water Splitting

Electrochemical water splitting, a crucial reaction for renewable energy storage, demands highly efficient and stable catalysts. Defect and interface engineering has been widely acknowledged to play a pivotal role in improving electrocatalytic performance. Herein, we demonstrate a facile strategy to construct sulfur vacancy (Sv)-engineered Co3S4/MoS2-interfaced nanosheet arrays to modulate the interface electronic structure in situ reduction with NaBH4. The abundant sulfur vacancies and well-arranged nanosheet arrays in Sv-Co3S4/MoS2 lead to pronounced electrocatalytic properties for hydrogen and oxygen evolution reactions (HER/OER) in an alkaline medium, with observed overpotentials of 156 and 209 mV at 10 mA cm-2, respectively. Additionally, as a bifunctional electrocatalyst, Sv-Co3S4/MoS2 requires a cell voltage of 1.67 V at 10 mA cm-2 for overall water splitting and exhibits long-term stability with activity sustained for more than 20 h. This study provides a novel approach to producing transition metal compound-interfaced electrocatalysts with rich vacancies under mild conditions, showcasing their potential for efficient water splitting applications.

Hydrothermal carbonization of biogas slurry and cattle manure into soil conditioner mitigates ammonia volatilization from paddy soil

Hydrothermal carbonization of biogas slurry and animal manure into hydrochar could enhance waste recycling waste and minimize ammonia (NH3) volatilization from paddy fields. In this study, cattle manure-derived hydrochar prepared in the presence of Milli-Q water (CMWH) and biogas slurry (CMBSH), and biogas slurry-based hydrochar embedded with zeolite (ZHC) were applied to rice-paddy soil. The results demonstrated that CMBSH and ZHC treatments could significantly mitigate the cumulative NH3 volatilization and yield-scale NH3 volatilization by 27.9-45.2% and 28.5-45.4%, respectively, compared to the control group (without hydrochar addition), and significantly correlated with pH and ammonium-nitrogen (NH4+-N) concentration in floodwater. Nitrogen (N) loss via NH3 volatilization in the control group accounted for 24.9% of the applied N fertilizer, whereas CMBSH- and ZHC-amended treatments accounted for 13.6-17.9% of N in applied fertilizer. The reduced N loss improved soil N retention and availability for rice; consequently, grain N content significantly increased by 6.5-14.9% and N-use efficiency increased by 6.4-16.0% (P < 0.05), respectively. Based on linear fitting results, NH3 volatilization mitigation resulted from lower pH and NH4+-N concentration in floodwater that resulted from the acidic property and specific surface area of hydrochar treatments. Moreover, NH3-oxidizing archaea abundance in hydrochar-treated soil decreased by 40.9-46.9% in response to CMBSH and ZHC treatments, potentially suppressing NH4+-N transformation into nitrate and improving soil NH4+-N retention capacity. To date, this study applied biogas slurry-based hydrochar into paddy soil for the first time and demonstrated that ZHC significantly mitigated NH3 and increased N content. Overall, this study proposes an environmental-friendly strategy to recycle the wastes, biogas slurry, to the paddy fields to mitigate NH3 volatilization and increase grain yield of rice.