| Hydrogen peroxide(H2O2)is widely used in chemical industry,environmental remediation and sustainable energy conversion as an environmentally friendly green oxide.Currently,industrial H2O2 production mainly uses anthraquinone process,but this technology is highly energy-intensive and environmentally polluting.Solar-driven photocatalytic technology uses renewable solar energy as energy supply to produce H2O2 through oxygen reduction and water oxidation pathways,which is a green alternative method for H2O2 production and is expected to solve the current energy shortage and environmental pollution problems.However,the low photocatalytic efficiency limits the practical application of photocatalytic production of H2O2.In this regard,it is crucial to develop efficient photocatalytic material systems.Boron-doped carbon nitride(BCN)has the advantages of visible light response,stable physicochemical properties and simple preparation,but it still suffers from the scientific problems of poor photogenerated charge separation and lack of reactive catalytic sites.To address these issues,this thesis focuses on the dual modulation of electrons and holes from the perspective of improving the efficiency of photogenerated charge separation and the introducing co-catalysts to increase the catalytic sites as follows:1.The effects of Ag and perylenimide(PDI)co-modification on the photogenerated charge separation properties of BCN and the performance of visible photocatalytic production of H2O2.First,PDI was modified on BCN by π-π assembly,and subsequently Ag nanoparticles were legally modified on BCN by photodeposition to obtain PD1/BCNAg nanocomposites.The PDI/BCN-Ag for H2O2 production rate could reach 143 μmol g-1 h-1 under visible light conditions,which is about 2.6 times that of BCN and 13 times that of g-C3N4.The enhanced activity could be attributed to the synergistic effect of PDI and Ag nanoparticles.S-scheme heterojunction was constructed with the PDI and BCN,which effectively promoted the carrier separation efficiency of BCN.The Ag nanoparticle as co-catalyst further trapped the photogenerated electrons and promoted the oxygen reduction reaction to occur.In addition,the "dual-channel" reaction pathway of oxygen reduction and water oxidation for H2O2 production was confirmed by active species capture experiments.2.The effects of FeOOH and CoOx nanoclusters co-modification on the modulation of electron and hole and visible photocatalytic H2O2 production performance were explored.Firstly,highly dispersed FeOOH nanoclusters were modified on the BCN by freeze-drying method.Subsequently,CoOx was further modified by in situ photodeposition to obtain the FeOOH and CoOx co-modified BCN.The H2O2 generation rate of optimal 0.75CoOx-BCN-1FeOOH can achieve 251 μmol g-1 h-1 with the 80%selectivity under visible light irradiation,which is 22 times higher than that of g-C3N4.The photogenerated charge transfer mechanism was analyzed by photophysical and photochemical means such as in situ transient absorption,and it was demonstrated that FeOOH nanoclusters can effectively capture photogenerated electrons and promote oxygen activation,and CoOx nanoclusters can capture photogenerated holes and catalyze water oxidation,both of which synergistically achieve dual modulation of electrons and holes,promoting photogenerated charge separation of BCN and meanwhile providing active sites for reduction-oxidation reactions.In addition,the introduction of FeOOH was found to change the oxygen reduction reaction path from an indirect two-step singleelectron reaction to a direct two-electron reaction,effectively improving the utilization of oxygen atoms.This thesis provides a feasible strategy for the design and synthesis of highly active BCN-based photocatalysts for H2O2 production from the perspective of photogenerated charge regulation and reaction catalysis,and also provides new ideas for revealing the reaction pathways for photocatalytic H2O2 production. |
