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Amorphous Co–Ni–B nanocatalyst with high electrocatalytic activity toward hydrogen evolution reaction (HER) in wide pH range was successfully synthesized. The content of Ni was varied by adjusting the molar ratio Ni/(Ni + Co) in Co–Ni–B from 10% to 50% to identify the most suitable composition for HER. Co-30Ni–B (with 30% Ni/(Ni + Co)) showed the highest catalytic activity and could reach a current density of 10 mA/cm 2 at just 170 mV in pH 7 and 133 mV in pH 14. It also exhibited a Tafel slope value of 51 mV/dec in pH 7 suggesting Volmer-Heyrovsky reaction mechanism for HER. The role of each element in improving the activity was justified with results from XPS, XAS and DFT calculations. It was observed that the presence of Ni promotes higher electron density at Co active sites of Co–Ni–B which in turn facilitates efficient reduction reaction to enhance HER rate. Co-30Ni–B could sustain 1000 cycles and prolonged hours of operation for about 40 h without losing activity making it an excellent low-cost electrocatalyst material. [ABSTRACT FROM AUTHOR]

Lattice location of B in TiO 2 is tuned to determine its effect on the photocatalytic activity of Co-B codoped TiO 2 . Sol–gel method was used to synthesize the samples. The concentrations of Co and B were first optimized by maximizing the photocatalytic activity for the monodoped (Co or B)-TiO 2 . In addition to the DFT calculations for discovering new energetic levels introduced in TiO 2 by codoping, various characterization techniques were used to determine the dopant lattice sites in TiO 2 and interactions between them; and also determining their consequences on electronic, morphological, structural, and optical properties. At low concentration of B-doping (1 at.%), B occupies the interstitial site (B int ), but as the concentration increases (2 at.% and 3 at.%) B also occupies substitutional O position (B sub ) in addition to B int to form TiO 2 containing B int+sub . Both these B-doped TiO 2 showed improved photocatalytic activity attributed to effective charge separation obtained for TiO 2 –B int due to the formation of shallow energy level while higher visible light absorption is achieved with TiO 2 –B int+sub owing to the presence of two deep energy levels in the band gap as confirmed by DFT calculations. In the case of Co doping, the band gap of TiO 2 is reduced but the recombination rates are always high and are caused by the formation of Co states in the band gap. For Co monodoped TiO 2 , the photocatalytic activity is low for all the concentrations considered, except for very low concentration of Co (0.1 at.%). Two opposite effects were observed when small amount of Co (0.1 at.%) was codoped with B int or B int+sub . In particular, the photocatalytic degradation rate of organic aqueous pollutants ( p -nitrophenol and rhodamine B dye) reduces for TiO 2 –Co–B int whereas it is enhanced remarkably for TiO 2 –Co–B int+sub as compared to (Co or B) monodoped (∼2.1 times) and undoped (∼7.8 times) TiO 2 . Higher photocatalytic activity observed in Co-doped TiO 2 –B int+sub is discussed in terms of the interactions of Co with B at two different lattice positions in TiO 2 and the synergistic effect created by higher visible light absorption and the improved charge separation. [ABSTRACT FROM AUTHOR]

Cu–N-codoped TiO 2 photocatalyst is synthesized by sol–gel method to obtain enhanced optical absorption in the visible region. Optimum concentrations of Cu and N were obtained by maximizing the photocatalytic activity for the monodoped (Cu or N) TiO 2 . These optimized concentrations were used for synthesizing (Cu, N)–codoped TiO 2 . The photocatalysts were characterized using XRD, micro-Raman, SEM, XPS, BET surface area analyzer, UV–vis diffuse reflectance spectroscopy and photoluminescence. XPS study suggests the incorporation of Cu 2+ into TiO 2 lattice, which assists N to substitutionally replace oxygen in codoped TiO 2 , while maintaining the anatase phase even after doping. N-doping creates minor variation in the energy band gap of TiO 2 reducing it upto 3.0 eV, while Cu doping was able to narrow the band gap to 2.2 eV mainly due to the localized levels of Cu-3d states and shifting of Ti-3d states to lower energy (due to oxygen vacancies) in the band-gap as deduced from XPS data and confirmed by the DFT calculation. In (Cu, N)–codoped TiO 2 , visible light absorption is higher than the other TiO 2 samples, a feature that is mainly attributed to the formation of an isolated intermediate band (IB) occurring due to the strong hybridization between Cu 3d and N 2p orbitals. This IB contributes to visible light absorption by two step optical transition with the first transition from valence band (VB) to IB and the second from IB to conduction band (CB). The dopant species may also act to reduce the charge carrier recombination by acting as the trapping sites for photogenerated charges. (Cu, N)–codoped TiO 2 was able to degrade Methylene Blue dye and p -Nitrophenol solution under light irradiation with significantly better rate in comparison to monodoped and undoped TiO 2 . High photocatalytic activity is attributed to the presence of IB in the energy band gap of TiO 2 , which creates the synergic effect by higher visible light absorption and lower recombination of photogenerated charges. [ABSTRACT FROM AUTHOR]