Boosting the catalytic activity of a step-scheme In_(2)O_(3)/ZnIn_(2)S_(4) hybrid system for the photofixation of nitrogen

In this study,a step-scheme photocatalytic system comprising one-dimensional In_(2)O_(3)nanorods and two-dimensional ZnIn_(2)S_(4)nanosheets was developed for the catalytic photofixation of nitrogen.The effects of the combination of In_(2)O_(3)with ZnIn_(2)S_(4)on the crystallinity,microstructure,optical absorption,and charge transfer behavior of the In_(2)O_(3)/ZnIn_(2)S_(4)hybrid photocatalysts were investigated.Benefiting from the synergistic effects of the photogenerated vacancies and a step-scheme charge separation mechanism,the In_(2)O_(3)/ZnIn_(2)S_(4)hybrid photocatalyst exhibited significantly enhanced catalytic activity compared to those of bare In_(2)O_(3)and pure ZnIn_(2)S_(4),and an optimized 50 wt%In_(2)O_(3)/ZnIn_(2)S_(4)hybrid sample was found to exhibit superior catalytic activity for the photofixation of N2,fixing 18.1±0.77 mg·L-1 of ammonia after exposure to simulated sunlight for 2 h.Crucially,the results of trapping experiments and electron paramagnetic resonance investigation to identify the active species confirmed that the catalytic nitrogen photofixation performance was highly correlated with the presence of·CO_(2)-radicals rather than photogenerated electrons,especially when methanol was used as a hole scavenger.In summary,the reported In_(2)O_(3)/ZnIn_(2)S_(4)hybrid photocatalysts exhibit both stability and high activity for the photofixation of N_(2),making them promising catalysts for sunlight-driven artificial N_(2)fixation.

Unveiling the critical role of TiO_(2)-supported atomically dispersed Cu species for enhanced photofixation of N_(2)to nitrate

Nitrate products are widely used in manufacturing as crucial raw materials and fertilizers.The traditional nitrate synthesis process involves high energy consumption and emission,thereby opposing the goals of zero-carbon emission and green chemistry.Thus,a sustainable roadmap for nitrate synthesis that uses green energy input,clean N sources,and direct catalytic processes is urgently required(e.g.,developing a novel photosynthesis system).Here,we synthesized TiO2-supported atomically dispersed Cu species for N_(2)photofixation to nitrate in a flow reactor.The optimized photocatalyst yielded a high nitrate photosynthesis rate of 0.93μmol h-1 and selectivity of~90%,which is superior to most of the values reported thus far.Further,experimental results and in-situ investigations revealed that the atomically dispersed Cu sites in the as-designed sample significantly enhanced the separation and transfer efficiency of photogenerated carriers,adsorption and activation of reactants,and the formation of chemisorbed O_(x)intermediates,thereby realizing the excellent photofixation of N_(2)to nitrate.

Nitrogen photofixation on holey g-C3N4 nanosheets with carbon vacancies under visible-light irradiation

Nitrogen photo fixation using g-C3N4-based photocatalysts have attracted abundant of attentions recently.Herein,in this study,holey g-C3N4(HGCN)nanosheets possess a good deal of carbon vacancies were prepared by means of thermally treating bulk g-C3 N4(BGCN)under an NH3 atmosphere.Characterization analysis revealed that the as-synthesized sample have identical crystal structure,la rger BET specific surface area,stronger reduction capability,and higher photogene rated charge carrier separation rate than that of BGCN.These properties may contribute to enhance the nitrogen photofixation activity.It was also found that the rate of NH4^+production for N2 photofixation of HGCN sample reached^25.54 mg L^-1 h^-1 g(cat)^-1,which is approximately^5.87 times higher than that of BGCN sample under optimal reactive conditions.Moreover,a plausible mechanism of HGCN for nitrogen photofixation process was illuminated in detail.

Atmospheric CO_(2) capture and photofixation to near-unity CO by Ti^(3+)-V_(o)-Ti^(3+) sites confined in TiO_(2) ultrathin layers

To realize efficient atmospheric CO_(2) chemisorption and activation,abundant Ti^(3+) sites and oxygen vacancies in TiO_(2) ultrathin layers were designed.Positron annihilation lifetime spectroscopy and theoretical calculations first unveil each oxygen vacancy is associated with the formation of two Ti^(3+)sites,giving a Ti^(3+)-V_(o)-Ti^(3+) configuration.The Ti^(3+)-V_(o)-Ti^(3+) sites could bond with CO_(2) molecules to form a stable configuration,which converted the endoergic chemisorption step to an exoergic process,verified by in-situ Fourier-transform infrared spectra and theoretical calculations.Also,the adjacent Ti^(3+)sites not only favor CO_(2) activation into COOH*via forming a stable Ti^(3+)–C–O–Ti^(3+) configuration,but also facilitate the rate-limiting COOH^(*)scission to CO^(*)by reducing the energy barrier from 0.75 to 0.45 e V.Thus,the Ti^(3+)-V_(o)-TiO_(2) ultrathinlayers could directly capture and photofix atmospheric CO_(2) into near-unity CO,with the corresponding CO_(2)-to-CO conversion ratio of ca.20.2%.

Promotion of activation ability of N vacancies to N2 molecules on sulfur-doped graphitic carbon nitride with outstanding photocatalytic nitrogen fixation ability

Nitrogen vacancies and sulfur co-doped g-C3N4 with outstanding N2 photofixation ability was synthesized via dielectric barrier discharge plasma treatment. X-ray diffraction, ultraviolet–visible spectroscopy, N2 adsorption, scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and temperature-programmed desorption were used to characterize the as-prepared catalyst. The results showed that plasma treatment cannot change the morphology of the as-prepared catalyst but introduces nitrogen vacancies and sulfur into g-C3N4 lattice simultaneously. The as-prepared co-doped g-C3N4 displays an ammonium ion production rate as high as 6.2 mg·L^-1·h^-1·gcat^-1, which is 2.3 and 25.8 times higher than that of individual N-vacancy-doped g-C3N4 and neat g-C3N4, respectively, as well as showing good catalytic stability. Experimental and density functional theory calculation results indicate that, compared with individual N vacancy doping, the introduction of sulfur can promote the activation ability of N vacancies to N2 molecules, leading to promoted N2 photofixation performance.

Single-atom-mediated electron islands boost photocatalytic CO_(2)chemical fixation

Photocatalytic cycloadditions of CO_(2)with epoxides are emerging as a significant platform for the green synthesis of valuable carbonates,where efficient catalytic systems with spatially separated charge carriers are demanded.Herein,a single p-block metal atom is proposed to be a candidate for photogenerated electron localization on a metal oxide substrate.By taking the Bi single-atom supported on ZnO nanosheet(Bi1/ZnO)as an example,we show that the Bi atom plays the role of an electron island in the sea of delocalized holes within ZnO.Meanwhile,the as-formed electron island could readily promote the rate-determining ring-opening process of cycloaddition reactions.Benefiting from the unique spatially separated electrons and holes,the Bi1/ZnO achieves a high yield of cyclic carbonates with almost 100%selectivity.This study provides a pioneering strategy for enhancing the performances of photocatalytic CO_(2)chemical fixation.