Photocatalytic Ammonia Production For Foliar Nitrogen Fertilizer With ZnO-based Catalysts

Nitrogen mainly originates from plants and is utilized to synthesize proteins and nucleic acids.Foliar nitrogen fertilizer can quickly supplement the nutrients needed for the growth of plants,which has the advantages of high efficiency and less environmental pollution.In this study,a novel photocatalytic foliar fertilization was proposed by combining photocatalytic ammonia production with foliar fertilization.Specifically,the photocatalytic supply solution for ammonia,containing catalysts and hole sacrifice agents,was sprayed on the leaves of plants.In this case,the photocatalytic evolution and plant absorption of ammonia were simultaneously realized.First of all,non-toxic and environmentally friendly catalyst ZnO was selected in this study,and then the performance of photocatalytic ammonia production was evaluated by modifying ZnO.Secondly,the feasibility and economic benefit of photocatalytic foliar fertilization method was evaluated preliminarily by using simulated leaves.Four-season-spinach with big leaves and rapid growth was selected as the experimental plant to investigate the effects of photocatalytic foliar fertilization on its growth.CZnO samples were fabricated by calcination with mechanical mixing.It was shown in the experiments that the introduction of C improved the photocatalytic performance and stability of ZnO.After calcination with glucose,the morphology of catalysts was different from that of the pristine ZnO.ZnO particles appeared on the surface of the rods.In the meanwhile,the specific surface area is 2.5 times that of the pristine ZnO,which was more conducive to the adsorption of nitrogen.The modified catalysts mainly had the following changes:a narrowed band gap declined photogenerated electron-hole recombination rate;an enhanced absorption capacity of visible light greatly improved the utilization of solar spectra;with the increase of photoresponse and charge transfer ability,more electrons can participate in the photocatalytic ammonia production.Cu modified CZnO catalysts were further prepared by microwave hydrothermal method.The efficiency of photocatalytic ammonia production over the optimal catalyst CuCZ-3.0%reached 4.96 mmol·g^-1·h^-1,which was 8.13 times as high as that of ZnO,1.64 times that of CZnO,and 2.73 times that of Cu ZnO-3.0%.Combined with the characterization results,the interfacial charge transfer induced by Cu and the“electron bridge”effect of C expanded the transfer path of photogenerated electrons,which resulted in the constrained recombination of photogenerated electrons and holes.Moreover,the optical properties and the performance of photocatalytic ammonia production significantly enhanced.In order to prove that photocatalytic ammonia production can be applied to foliar fertilization,the photocatalytic supply solution for ammonia,containing CuCZ-3.0%and glycerol,was sprayed on simulated leaves,and it was calculated that the total amount of nitrogen fertilizer released by this method was about 443.1 g·ha^-1·day^-1.In addition,photocatalytic foliar fertilization was used to supplement nitrogen fertilizer for spinaches in pot experiments,in which spinaches could grow normally and there was no phenomenon of malnutrition such as bolting.