Modification Of Nano-TiO₂and Novel Red Phosphorous Photocatalysts For Photocatalytic Hydrogen Production From Water

H2energy is considered as an ideal candidate for the green energy carrier of the futuredue to its high energy content, recycling possibility and environmental-friendliness. Watersplitting for H2generation over semiconductor using solar energy has been regarded as achallenging approach for producing hydrogen. Nano-TiO2is the most extensively investigatedsemiconductor material and have wide applications in many fields, including solar watersplitting, photodegradation of pollutants, air purification and bacillus resistance. However,bare TiO2has a wide band gap (only absorb UV light), and suffers from narrow light-responserange, rapid recombination rate of photoinduced electron/hole pairs and relatively smallspecific surface area, which greatly limits its large-scale applications. In this paper, our mainideas are modifying the TiO2surface property, tuning its morphological structure, separatingthe charge carriers and modifying the novel visible-light-active red phosphorus photocatalystto enhance the photocatalytic H2evolution activity.(1) Co(OH)2clusters modified TiO2nanocomposite photocatalysts were fabrication by afacile precipitation method using Degussa P25powder and CoCl2as precursors. The effect ofCo(OH)2loading content on the photocatalytic H2evolution activity of the as-preparedsamples was investigated in methanol aqueous solution. The results showed that thephotocatalytic H2evolution activity of TiO2was significantly enhanced after the Co(OH)2modification. The optimum Co(OH)2loading content was measured to be0.25mol%, givinga H2evolution rate of1946μmol·h-1·g-1, being about23times of that on pure TiO2. Thisenhancement of photocatalytic H2evolution was attributed to the Co(OH)2clusters depositedon TiO2surface, which can act as electron traps and favor the transfer of CB electrons fromTiO2to Co(OH)2clusters, thus facilitating the charge carrier separation and enhancing thephotocatalytic H2evolution activity.(2) Cu(OH)2/TNTs nanocomposite photocatalysts were successfully prepared by loadingnano-Cu(OH)2on TNTs suface via a hydrothermal precipitation process using TiO2nanotubesand Cu(NO3)2as precursors. The effects of Cu(OH)2loading, amount of catalyst on thephotocatalytic H2evolution performance of Cu(OH)2/TNTs were investigated in aqueousmethanol solution under a400W high pressure Hg lamp irradiation. The results show that,compared with pure TNTs, the TNTs loaded with highly dispersed8wt%Cu(OH)2exhibitedremarkably improved activity for hydrogen production and the largest quantity of evolvedhydrogen was ca.14.94mmol·h-1·g-1. This high activity is attributed to the strong synergisticfunction of Cu(OH)2/TNTs, including suitable potential of Cu(OH)2/Cu(E0=-0.222V) between conduction band (-0.260V) of TNTs and the reduction potential of H+/H2(E0=0.000V), aunique tubular microstructure of TNTs coated with nano-Cu(OH)2, large BET specific surfacearea and high dispersion of Cu(OH)2.(3) A facile and green one-step method was used to prepare titanate nanotube/graphene(TNT/GR) photocatalysts via an alkaline hydrothermal process using graphene oxide and P25as precursors. The photocatalytic performance was evaluated by H2generation from watersplitting under Xe-lamp illumination. The results showed that graphene can act as an effectiveco-catalyst for enhancing the photocatalytic H2evolution activity of TiO2nanotubes and itscontent had a great influence on the photocatalytic H2evolution activity. A significantlyenhanced photocatalytic activity for H2evolution (12.1μmol·h-1) was obtained over thecompostion-optimized TNT/GR composite (with1.0wt%GR), two times higher than that ofpure TNTs (4.0μmol·h-1). The introduction of GR into TNTs greatly enhanced itsphotocatalytic H2evolution activity, which is attributed to the highly efficient photoinducedcharge separation.(4) Efficient photocatalytic H2generation was successfully realized on Ni(OH)2clustersmodified red phosphorus photocatalyst from methanol aqueous solution under a wide range ofvisible light irradiation. Ni(OH)2clusters was deposited on red phosphorus suface by aone-step liquid precipitation method using red phosphorus and Ni(NO3)2as precursors.Ni(OH)2clusters could function as efficient co-catalysts and capture the photoexcitedelectrons, thus prolonging the lifetime of photogenerated charge carriers. The optimumNi(OH)2loading content was0.5wt%, yielding a H2evolution rate of1.65μmol·h-1, being2.12times of that on1wt%Pt loaded red phosphorus (0.78μmol·h-1). This improvedphotocatalytic activity was attributed to that the potential of Ni2+/Ni (-0.23V) is slightly lowerthan the conduction band of red phosphorus (-0.25V), meanwhile it is higher than thereduction potential of H+/H2(0.00V), which facilitates the migration of the excited electronsfrom red phosphorus to Ni(OH)2clusters and the reduction of H+to H2, thus enhancing thephotocatalytic water splitting performance for H2evolution.