| Ammonia has long played a key role in the basic survival and healthy development of human society.Ammonia is not only the main production component of artificial fertilizer in modern agriculture,but also one of the initial components in the chemical industry.In addition,ammonia is a kind of zero-carbon fuel with large hydrogen capacity,which is of great significance to alleviate the energy crisis and also provides feasibility for the realization of carbon neutrality.In industry,the traditional ammonia synthesis engineering mainly relies on the Haber-Bosch process,which needs high temperature and pressure and the iron-based catalyst to trigger the reaction of nitrogen and hydrogen.The demand for energy consumption is very high,which is detrimental to the green development of the environment.Therefore,it is urgent to develop a new type of synthetic ammonia technology that is environmentally friendly and has low energy consumption.Photocatalytic nitrogen fixation is a greener,more ecological,and more sustainable strategy.Among many semiconductor materials,transition metal oxide W18O49 has been applied in the field of photocatalytic nitrogen fixation due to its suitable band gap and fascinating advantage of containing oxygen vacancies.However,it suffers from the deficiencies of easy recombination of photogenerated carriers and few reaction sites for N2 adsorption and activation,so it needs to be modified by doping and constructing heterojunctions to enhance photocatalytic activity.The specific work is as follows:（1）Fe-W18O49 nanorods were synthesized by a mild solvothermal method using tungsten hexachloride and anhydrous ethanol as raw materials and ferric chloride as a dopant.Cu O nanoparticles were synthesized by a thermochemical precipitation method with copper sulfate as the copper source and sodium hydroxide as the precipitant.Finally,Cu O nanoparticles were successfully loaded on Fe-W18O49 nanorods by a simple impregnation method to form the Z-scheme heterojunctions.By simulating sunlight irradiation,20%Cu O/Fe-W18O49composites have the best nitrogen fixation efficiency of about 88.25μmol g-1 h-1 without the involvement of any sacrificial reagent,which is 4.4 times that of pure W18O49.The improvement of photocatalytic performance benefits from the presence of oxygen vacancies,which enhance the adsorption and activation of N2,and also benefits from the construction of the Z-scheme heterojunctions,which promotes photogenerated carriers to distribute electrons to the conduction band with a higher reduction ability.（2）Fe-W18O49 nanorods with oxygen vacancies were obtained by doping and modifying with iron elements using W18O49 synthesized by a solvothermal method as the main material.Cu Bi2O4 microrods were synthesized by a solvothermal method with copper nitrate as the copper source,bismuth nitrate as the bismuth source,and sodium hydroxide as the alkali source.Finally,the Z-scheme heterojunctions CBO/Fe-W18O49 were successfully constructed by the impregnation method.15%CBO/Fe-W18O49 composites have the best nitrogen fixation efficiency of about 101.71μmol g-1 h-1 under simulated solar irradiation and without the involvement of any sacricial reagents,which is 5.1 times that of pure W18O49.The tests of DRS,PL,IT,and EIS show that 15%CBO/Fe-W18O49composites have higher photoabsorption,photocurrent density,and lower possibility of photogenerated carrier recombination.In addition,the presence of Z-scheme heterojunctions recombine electrons and holes with weak redox ability in the composites and retain electrons and holes with high redox ability.（3）In-W18O49 nanorods with oxygen vacancies were synthesized by a solvothermal method by adding indium chloride dopant into the precursor tungsten hexachloride alcohol solution.The amorphous Co B nano-alloys without noble metals were synthesized by the redox method using cobalt acetate as the cobalt source and sodium borohydride as the reducing agent.Finally,Co B/In-W18O49 Schottky junctions were successfully constructed by a simple impregnation method.By simulating sunlight irradiation with sodium sulfite as the sacrificial reagent,15%Co B/In-W18O49 composites have the best nitrogen fixation efficiency,of about 121.15μmol g-1 h-1,which is higher than that of both Co B and In-W18O49 monomeric materials.Co B has an important contribution to the improvement of the light absorption capacity of the composites.The presence of oxygen vacancies in In-W18O49 promotes the adsorption and activation of N2 on the surface,and the Schottky junction formed by the close contact between Co B and In-W18O49 contributes to the rapid transfer of electrons from In-W18O49 to Co B.These comprehensive effects improve the photocatalytic nitrogen fixation efficiency of Co B/In-W18O49 composites. |
