Noble metal/semiconductor nanocomposites play an important role in high efficient photocatalysis. Herein, we demonstrate a facile strategy for fabrication of hollow Pt-ZnO nanocomposite microspheres with hierarchical structure under mild solvothermal conditions using Zn (CH(3)COO)(2)·2H(2)O and HPtCl(4) as the precursors, and polyethylene glycol-6000 (PEG-6000) and ethylene glycol as the reducing agent and solvent, respectively. The as-synthesized ZnO and Pt-ZnO composite nanocrystals were well characterized by powder X-ray diffraction (XRD), nitrogen-physical adsorption, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS), and photoluminescence (PL) emission spectroscopy. It was found that Pt content greatly influences the morphology of Pt-ZnO composite nanocrystals. Suitable concentration of HPtCl(4) in the reaction solution system can produce well hierarchically hollow Pt-ZnO nanocomposite microspheres, which are composed of an assembly of fine Pt-ZnO nanocrystals. Photocatalytic tests of the Pt-ZnO microspheres for the degradation of the dye acid orange II revealed extremely high photocatalytic activity and stability compared with those of pure ZnO and corresponding Pt deposited ZnO. The remarkable photocatalytic performance of hollow Pt-ZnO microspheres mainly originated from their unique nanostructures and the low recombination rate of the e(-)/h(+) pairs by the platinum nanoparticles embedded in ZnO nanocrystals.

The development of highly efficient catalysts for ambient formaldehyde (HCHO) destruction is of great interest for indoor air purification. Here, we show that a sodium (Na)-doped iridium (Ir) catalyst (Ir/TiO2) is a highly active catalyst for the catalytic oxidation of HCHO at room temperature. We observed that Na addition dramatically enhanced the activity of the Ir/TiO2-R catalyst, and 100% HCHO conversion was achieved over Na-Ir/TiO2-R catalyst at a gas hourly space velocity of 100,000 h–1 and HCHO inlet concentration of 120 ppm at 25 °C. The Ir/TiO2 and Na-Ir/TiO2 catalysts were characterized using X-ray powder diffraction, Brunauer–Emmett–Teller surface area testing, high-angle annular dark-field scanning transmission electron microscopy, H2 temperature-programmed reduction (TPR), X-ray absorption fine structure, X-ray photoelectron spectroscopy, and CO-TPR. The characterization results show that the addition of Na species had no influence on Ir dispersion on the TiO2 surface but greatly promoted the activation of both chemisorbed oxygen and H2O. The reaction mechanism of HCHO oxidation was investigated by using in situ diffuse reflectance infrared transform spectroscopy. The results show that the reaction mechanisms on Ir/TiO2-R and Na-Ir/TiO2-R both followed the direct formate oxidation pathway (HCHO → HCOO + OH → CO2 + H2O), and the activated oxygen species mainly participated in the formate formation step while the activated OH groups were primarily responsible for the subsequent formate oxidation. Because of the improved capacities for the activation of oxygen and H2O induced by Na addition, the Na-Ir/TiO2 catalyst demonstrated much better performance than Ir/TiO2 for ambient HCHO oxidation.

Highlights d An inducible CRISPRi system identifies rate-limiting enzymes d E. coli metabolism is robust against CRISPRi-knockdowns of enzymes d CRISPRi enforces specific metabolome and proteome responses d Regulatory metabolites buffer CRISPRi-knockdowns