Preparation Of Graphitic Carbon Nitride Based Nanocomposites And Their Photocatalytic Performance Towards Water Splitting

In the past few decades,the increase of energy demand has led to the increase of fossil fuel consumption,which has aroused people's concern about the environment problem,thus greatly promoting the research and development of alternative renewable energy.Solar photocatalytic hydrogenation is a promising green and renewable energy production process.At present,a large number of studies are devoted to the development of efficient,reliable,cheap,sustainable and eco-friendly catalytic systems.The semiconductor photocatalytic technology driven by solar energy is becoming an effective way to solve energy and environmental problems with its unique advantages,such as renewable,clean and safe.Photocatalyst is necessary to effectively convert solar energy into chemical energy.In the past.TiO2 as the main photocatalyst has been widely studied and successfully implemented in commercial applications.However,only ultraviolet light with a wavelength less than about 388 nm(only a small part of the solar spectrum(3-5%))can excite electrons in the valence band of titanium.Therefore,the development of many new photocatalysts with photocatalytic activity driven by visible-light has become a very hot research topic in the field of photocatalysis.Graphite phase carbon nitride(g-C3N4)as an attractive photocatalyst for water splitting has been applied in many fields such as sensors,artificial light synthesis and CO2 emission reduction.Graphite carbon nitride(g-C3N4)is an excellent n-type semiconductor with a band gap of 2.7 eV.It has good response to visible light,non-toxic.thermal stability,chemical stability and other advantages,and is suitable for many fields including photocatalysis.Although g-C3N4 has a suitable band gap position.light-induced electron-hole pair recombination rapidly leads to inefficient photocatalytic performance.In this paper,a semiconductor-semiconductor heterojunction is formed by coupling with g-C3N4 by selecting a suitable semiconductor to improve its photocatalytic water splitting performance.(1)A novel nonprecious metal-based P doped g-C3N4(PCN)/polyaniline(PANI)/BaTiO3(BTO)(PPB)ternary photocatalyst in hollow architecture is rationally designed and prepared by a combined wet-chemical and thermal treatment strategy.The as-synthesized PCN/PANI/BTO photocatalyst reveals boosted improvement for visible-light absorption,separation efficiency of photoinduced charge carrier and charge injection to the photocatalytic product,resulting in enhanced visible-light photocatalytic hydrogen production activity of 602 ?mol h-1 g-1 that is 21-fold of pristine g-C3N4(3055 ?imol h-1g-1 with 3wt%Pt)and an apparent quantum efficiency of 4.16%(16.61 with 3wt%Pt)at 420 nm.The excellent photocatalytic activities are ascribed to the synergetic effects of PCN,PANI and BTO due to the formation of Z-scheme heterojunction between PCN/PANI and polarization of ferroelectric BTO,which is responsible to the fast separation and slow recombination of photoinduced electron-hole pairs.The photoinduced electrons are concentrated on intermediate p-type PANI while holes are left on lateral n-type PCN involved in the Z-scheme,resulting in the retention of high oxidation-reduction potentials.Moreover,this approach to enhance photocatalytic activity by constructing Z-scheme heterojunction and surface polarization is considered to be able to expand to other photosystem,which pave a new avenue for rational design and synthesis of novel photocatalyst.(2)A novel g-C3N4/?-Fe2O3/Co-Pi(CFP)hollow structure ternary photocatalyst was synthesized by coating ?-Fe2O3 nanocrystals on the surface of g-C3N4,and Co-Pi was further deposited on the surface of the composite.The photocatalytic hydrogen production rate of CFP is 450 ?mol h-1 g-1,which is 15.7 times that of the original g-C3N4,and the apparent quantum efficiency is 3.11%.As a photosensitizer,?-Fe2O3 can effectively improve the absorption capacity of g-C3N4 to visible light.A z-scheme heterojunction was formed between g-C3N4 and ?-Fe2O3.The photoexcited electrons were concentrated in the conducting band of g-C3N4,and the holes were left in the valence band of ?-Fe2O3,resulting in the high oxidation-reduction potential of?-C3N4/?-Fe2O3 composite.Photoelectrodeposition of Co-Pi on the surface of-g-C3N4/?-Fe2O3,Co-Pi as a hole storage agent can effectively improve the separation of electron-hole pairs of g-C3N4/?-Fe2O3/Co-Pi composite photocatalyst and promote its photocatalytic water splitting performance.