Efficient visible light photodegradation of Methylene blue using TiO 2 -graphene based composites has been reported. DFT calculations corroborate the mechanism for Ti-O-C bond formation, leading to an additional band edge and band gap tuning. AbstractHere we report experimental and theoretical study of two TiO 2 -graphene oxide (TG) and TiO 2 -reduced graphene oxide (TR) composites synthesized by a facile and ecological route, for enhanced visible light (~470nm) photocatalyc degradation of Methylene Blue (MB) (99% efficiency), with high rate constant value (1800% over bare TiO 2 ). TG couples TiO 2 nanopowder with Graphene Oxide (GO) while TR couples it with reduced graphene oxide (RGO). The present study, unlike previous reports, discusses never before reported double absorption edges obtained for both TG (3.51 eV and 2.51 eV) and TR (3.42 eV and 2.39 eV) composites, which marks the reason behind feasible visible light (2.56 eV) induced photocatalysis. TiO 2 domains in the composites dominate the higher band edge, while GO/RGO domains explain the lower band edge. Formation of Ti-O-C bond in both TG and TR drives the shifting up of the valence band edge and reduction in band gap. Further, these bonds provide a conductive pathway for charge carriers from TiO 2 nanopowder to the degrading species via the GO/RGO matrix, resulting in decreased charge carrier recombination in TiO 2 and enhanced efficiency.To attest that the developed theory is proof-positive, density function theory (DFT) calculations were performed. DFT obtained energetics and electronic structures support experimental findings by showcasing the play of Ti-O-C bond, resulting in double band edge phenomenon in composites.Finally, the mechanism behind MB degradation is discussed comprehensively and the effect of weight percent of GO/RGO in composite on rate constant and photodegradation efficiency has been studied experimentally and explained by developing analytical equations. 4 promising as it simultaneously possesses excellent absorptivity, transparency, conductivity and reachability, which could assist effective photodegradation of pollutants.There is a pool of reports showing the enhanced photocatalytic activity of TiO 2 nanoparticles with graphene composites for the degradation of organic molecules and photocatalytic splitting of water under UV light. 22, 28-38 Enhanced photocatalytic activity was attributed to the synergetic effect between graphene and TiO 2 nanoparticles, because graphene acts as an excellent electron acceptor and transporter, the Ti-O-C bond open up an easy path for charge transfer which remarkably decreases the recombination of electron−hole pairs. 3 Although claiming good efficiency, many of these reports are based on usage of un-ecological UV light and suffer from low kinetics (k value). [28][29][30] Realizing the importance of efficient visible light photodegradation, there are few reportes which show enhanced photocatalytic activity of TiO 2 -GO/RGO composites under visible light. 39-42 The results and application part is...

We have undertaken first-principles electronic structure calculations to show that the chemical functionalization of two-dimensional hydrogenated silicene (silicane) and germanene (germanane) can become a powerful tool to increase the photocatalytic water-splitting activity. Spin-polarized density functional theory within the GGA-PBE and HSE06 types of exchange correlation functionals has been used to obtain the structural, electronic, and optical properties of silicane and germanane functionalized with a series of nonmetals (N, P, and S), alkali metals (Li, Na, and K) and alkaline-earth metals (Mg and Ca). The surface-adsorbate interaction between the functionalized systems with H2 and O2 molecules that leads to envisaged hydrogen and oxygen evolution reaction activity has been determined.

Electronic and optical properties of CH3NH3Pb1−xSnxI3 are determined using DFT. Sn doping narrows band gap allowing 850 nm absorption. Delocalized Sn-5p induced electronic states increase mobility. 50% Sn doping is revealed as optimum composition.

Spin polarized density functional theory within the GGA-PBE and HSE06 approach for the exchange correlation term has been used to investigate the stability and electronic properties of nitrogen and boron impurities in single layers of silicane and germanane. We have observed that these impurities have lower formation energies in silicane and germanane when compared to their counterparts in graphane. We have also noticed that the adsorption of H atoms in the vicinity of defects stabilizes the system. In addition, we have shown that the electronic properties of silicane and germanane can be tuned when N and B are incorporated in the Si and Ge network. N-doping and B-doping give rise to n-type and p-type semiconductor properties. However, the adsorption of H atoms quenches the doping effects.

Spin-polarized density functional theory and norm conserving fully separable pseudopotentials are used to study the structural and electronic properties of atomic oxygen defects (substitution and adsorbed) as well as the O 2 adsorption in (3,3) and (5,0) BC 2 N nanotubes. For the adsorbed molecules, detailed calculations are performed by introducing the van der Waals interactions through the B97-D functional proposed by Grimme. The most stable configuration for the adsorbed oxygen atom is in the interstitial site binding with boron and carbon atoms (BAOAC I configuration), and for the substitutional doping, the most stable configuration occurs when the oxygen substitutes the nitrogen atom (O N ). For these two defects, the calculated formation energies are À1.67 and 0.62 eV, respectively. The calculated electronic band structures show that the O N defect leads the system to exhibit a p-type semiconductor character, whereas the interstitial oxygen atom does not introduce any significant changes in the electronic states near the band gap region. The interaction between the nanotubes and the O 2 molecule is investigated by the adsorption of the molecule in the inner and outer surfaces of the nanotubes. The calculated binding energies show that the molecule in the triplet state is physically adsorbed in the inner surface with the molecular axis perpendicular to the nanotube axis. For the molecule in the singlet state, the most stable configuration occurs when the molecule interact with the outer surface and bind (weakly) with a boron atom. We also observe spin transference between the molecule and the tube leading the boron carbonitrides (BCN) nanostructures as candidate to storage and detect the O 2 molecules.

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Spin polarized density functional theory is used to investigate the incorporation of substitutional Si atoms in the zigzag (5,0) and in the armchair (3,3) BC(2)N nanotubes (NTs). Our results show that the Si impurities in BC(2)N NTs have lower formation energy when compared to Si in carbon and boron nitride NTs. In neutral charge state, Si in the boron site (Si(B)) presents a spin split with two electronic levels within the NT band gap and it gives rise to a net spin magnetic moment net of 1mu(B). Si in the nitrogen site (Si(N)) introduces electronic levels near the top of the valence band that lead the system to exhibit acceptor properties, which suggest the formation of defect-induced type-p BC(2)N NTs. The defective levels for Si in the two nonequivalent carbon atom sites (Si(CI) and Si(CII)) are resonant with the valence and conduction bands, respectively. The calculations of formation energy in charge state show that for all the available values of the electronic chemical potential, Si(CI) and Si(CII) have lower formation energy in neutral charge state, while Si(B) and Si(N) present lower formation energy in neutral or single negative charge state depending on the position of the electronic chemical potential.