Enhancing the electrocatalytic performance of SnX2 (X = S and Se) monolayers for CO2 reduction to HCOOH via transition metal atom adsorption: a theoretical investigation.

Exploring highly efficient, stable, and low-cost electrocatalysts for CO2 reduction reaction (CRR) can not only mitigate greenhouse gas emission but also store renewable energy. Herein, CO2 electroreduction to HCOOH on the surface of SnX2 (X = S and Se) monolayer-supported non-noble metal atoms (Fe, Co and Ni) was systematically investigated using first-principles calculations. Our results show that Fe, Co and Ni adsorbed on the surface of SnX2 (X = S and Se) monolayers can effectively enhance their electrocatalytic activity for CO2 reduction to HCOOH with low limiting potentials due to the decreasing energy barrier of *OOCH. Moreover, the lower free energy of the *OOCH intermediate on the surface of TM/SnX2 (X = S and Se) monolayers verifies that the electroreduction of CO2 to HCOOH prefers to proceed along the path: CO2 → *OOCH → *HCOOH → HCOOH. Interestingly, SnX2 (X = S and Se) monolayer-supported Co and Ni atoms prefer the HCOOH product with low CRR overpotentials of 0.03/0.01 V and 0.13/0.05 V, respectively, showing remarkable catalytic performance. This work reveals an efficient strategy to enhance the electrocatalytic performance of SnX2 (X = S and Se) monolayers for CO2 reduction to HCOOH, which could provide a way to design and develop new CRR catalysts experimentally in future.

[Kinetics of alkylphenols degradation in aqueous phase with excilamp irradiation].

The 206 nm irradiation from excilamp was able to directly photo-degrade 4-nonylphenol (4-NP) and 4-octylphenol (4-OP), but it could not oxidize them completely into CO2. Under the same irradiation condition, the removal efficiency of 4-OP was higher than that of 4-NP. Pseudo-first order kinetic model and modified kinetic model were used to fit the kinetics of photo-degradation process, and the direct photolysis rate constants under 206 nm UV irradiation were obtained. The experimental results demonstrated that the photolysis rate constant was higher at lower initial concentration of alkylphenols. Two kinetic models were appropriate for the direct photolysis of alkylphenols at low concentration, but the modified model did not fit for high concentrations. Degradation rate can be obviously enhanced when adding H2O2 into the reaction, but the TOC removal was distinct only when the dosage of H2O2 was high. At last, we concluded that the direct photolysis rate constant k(d) was 0.032 8 min(-1) and the reaction rate constant k(pH) between 4-OP and H2O2 was 17.4520 L x (mol x min)(-1).