Photoreduction And Mechanism Of Diluted CO₂ On Nickel-based Nanomaterials With Microstructure Regulation

Heavy reliance on fossil fuels results in ever-increasing CO₂ emission and then causes energy crisis and global environmental burden.Converting the“waste”CO₂ into valuable chemicals by the photocatalytic process shows great promise for simultaneously alleviating energy and environmental troubles.Despite the progress that has been made,there are still some challenges to overcome.Firstly,the CO₂ conversion efficiency is still fairly low due to their thermodynamical stability with high dissociation energy of the C=O bond(ca.750 kJ mol-1).Secondly,the sluggish kinetic process with multielectron reaction and protons transfer process greatly impede the high selectivity of a specific product among many possible reaction species.In addition,most works in the laboratory require high-purity CO₂ gases,however,the CO₂concentration in the actual industrial exhaust gas is only 5-15%.In this case,directly realizing the photoreduction of low-concentration CO₂ meanwhile avoiding the high-energy-consuming CO₂ purification process has important scientific significance for practical application research.The development of efficient,cheap and stable catalytic materials is a scientific problem that needs to be solved urgently.The studies have found that the key factors affecting the performance of the catalyst are mainly the surface adsorption of the target,the number of active sites and the intrinsic catalytic activity.By optimizing the external microenvironment and internal microstructure of the catalyst,it is possible to control the micro-nano morphology of the catalyst,absorb more reaction gases,increase active sites,optimize the electronic structure,and then improve their intrinsic catalytic activity.Based on the fact that nickel-based materials are effective catalysts for CO₂ photoreduction,we use nickel-based nanomaterials as a research platform.We prepared lattice-strained nanomaterials through element doping,metal defects and morphology control strategies to improve the catalyst.The micro-chemical structure and surface micro-environment further clarify the structure-activity relationship,reveal the law of improving catalytic performance,and provide a theoretical basis for the practice application of catalysts.The main research contents of this paper are as follows:(1)Improve the microstructure and microenvironment of the catalyst by modification of the catalyst to improve the performance of CO₂ photoreduction.Inspired by natural photosynthesis,a bioinspired artificial system is constructed based on Zr O₂ nanoframes(ZFs)and metalloporphyrin to mimic trees morphology.The robust backbone of the framework and the bio-inspiring porphyrins anchored on the surface of ZFs function as the strong trunks and well-ordered leaves of the trees,respectively.The biomimetic system achieved an evolution yield of 35.3?mol during 3h reaction with 93.1%CO selectivity and 1.84%CO apparent quantum efficiency(A.Q.E.),which is about 60.8 times larger than that of mere pure porphyrin(Ni)(0.58?mol).When the CO₂ concentration is reduced to 0.1 atm,the CO production and selectivity of ZFs-TCPP-Ni still reached 15?mol and 88.0%in the first hour.Detailed analysis reveals that the catalytic system could not only achieve fast separation of the photogenerated carriers and effective CO₂ activation but also possess suitable energy levels,which could efficiently transfer electrons to the Ni catalytic sites to improve the photocatalytic activity.Furthermore,the robust supporting of frameworks and the strong binding of the Zr atoms and carboxyl groups of porphyrins could be strongly answered to the good recycling tests.This work highlights the important role of catalyst's structure and surface interface microenvironment in photocatalytic CO₂ reduction,and outlines possible strategies for the other biomimetic manufacture.(2)Lattice strain was investigated by adjusting the content of the nickel in Ni Se,and was applied to the high-efficiency diluted CO₂ photoreduction.The XRD refined data combined with the classic stress analysis method(Williamson-Hall method)show that Ni vacancies in the crystal lattice leads to lattice distortion,which makes for the obviously lattice strain.Under visible light irradiation,Ni_1-xSe nanoflowers exhibit the CO generation yield and selectivity of 16.42?mol and 90.7%within 3 hours,respectively.Even the CO₂ concentration reduced to 0.1 and 0.05atm,the CO selectivity of Ni_1-xSe can still reach about 72.7%and 61.7%.The experimental results show that lattice-strained Ni_1-xSe not only has an appropriate energy level structure to achieve photo-generated carrier separation,but also can significantly enhance the uptake of CO₂,which finally achieve high-performance of diluted CO₂ reduction.This work provides rational avenue for design and synthesis of high-efficient catalysts from the perspective of microstructure.(3)Lattice-strained nickel hydroxide nanosheets(NS)were constructed via a vanadium-doped strategy towards improvement of photoreduction of diluted CO₂.X-ray absorption fine structure spectroscopy and Williamson–Hall analysis based on X-ray diffraction well reveal the formation of the lattice strain on the surface of the Ni(OH)₂ NS.Consequently,the lattice-strained samples exhibited the highest CO production rate of 20745?mol g^-1 with a CO selectivity of 97%in pure CO₂,which is almost 4 times and 1.3 times than that of its parent Ni(OH)₂ NS.Even in the diluted CO₂(0.1 atm),lattice-strained catalysts exhibit a CO production rate of 5800?mol g^-1h^-1 with a CO selectivity of 91.3%,surpassing most previous works in pure CO₂.Further characterization revealed that lattice strain can greatly improve the CO₂ adsorption and activiation,and separation efficiency of photogenerated carries,thus leading to the enhancement of photocatalytic activity.This work discloses a clear atomic-level correlation between lattice strain and diluted CO₂ photoreduction.(4)Ultrathin Ni₂(OH)(PO₄)nanotubes(NTs)were prepared through hydrothermal route for photoreduction of CO₂ under real sunlight,which were used to explore the possibility of practical application.The prepared Ni₂(OH)(PO₄)NTs exhibit a 11.3?mol/h CO production rate with 96.1%CO selectivity.Interestingly,Ni₂(OH)(PO₄)NTs have a positive impact on the facilitation of photoreduction in diluted CO₂.Notably,when the system is performed under real sunlight,Ni₂(OH)(PO₄)NTs afford an accumulated CO of ca.26.8?mol with 96.9%CO selectivity,exceeding most previous inorganic catalysts under simulated irradiation in the laboratory.Our experimental results demonstrate that the multisynergetic effects induced by surface-OH and the lattice strain serve as highly active sites for CO₂ molecular adsorption and activation as well as electron transfer,hence enhancing photoreduction activity.Therefore,this work provides experimental basis that CO₂ photocatalysis can be put into practical use.