Round-the-Clock Adsorption-Degradation of Tetracycline Hydrochloride by Ag/Ni-TiO2.

The synergy of adsorption and photocatalysis is a good method to remove organic pollutants in wastewater. In recent decades, persistent photocatalysis has gained considerable interest for its ability to sustain the catalytic degradation of organic pollutants in the dark. Herein, we report three different TiO2 nanomaterials to remove tetracycline hydrochloride (TCH) in solution. We found that the removal ability of TiO2, Ni-TiO2, and Ag/Ni-TiO2 is 8.8 mg/g, 13.9 mg/g and 23.4 mg/g, respectively, when the initial concentration of TCH is 50 mg/L. Chemical adsorption could be the rate-determining step in the TCH adsorption process. Moreover, Ag nanoparticles dispersed on Ni doped TiO2 surface act as traps to capture photo-generated electrons upon illumination with indoor light. The holes in Ag/Ni-TiO2 serve as critical oxidative species in TCH degradation under dark conditions. This work provides new insights into the design of persistent photocatalysts that can be activated by weak illumination and degrade organic pollutants in wastewater after sunset.

Insights into the roles of superficial lattice oxygen in formaldehyde oxidation on birnessite.

K+-modified birnessite materials were constructed to remove formaldehyde (HCHO) in this work. The introduction of K+ led to weakening of the Mn-O bonds and enhanced the migration of superficial lattice oxygen, resulting in improved redox properties and catalytic activity. MnO2-3K with the largest specific surface area and greatest abundance of superficial lattice oxygen showed the best catalytic performance at 30-130 °C. The operando analyses reveal that HCHO is primarily activated to dioxymethylene (DOM) and subsequently converted to formate species (*COOH). The accumulation of formate species caused a decline in catalytic performance during extended testing at 30 °C, a challenge that could be mitigated by raising the temperature. Theoretical studies disclose that the *COOH → *H2CO3 step with the largest energy barrier is the rate limiting step for HCHO deep decomposition. Molecular oxygen could be activated at oxygen vacancies to replenish the depleted lattice oxygen after decomposition of carbonate species (*H2CO3) and CO2 and H2O desorption. The adsorbed oxygen and water did not limit the deep oxidation of HCHO. This research presents a promising approach for designing highly efficient, non-noble metal catalysts for formaldehyde degradation.