Rational design of manganese ferrite-graphene hybrid photocatalysts: Efficient water splitting and effective elimination of organic pollutants

Graphene oxide (GO):MnFe2O4 (Mn) hybrids synthesized by sol-gel hydrothermal (453 K, 48 h); and annealed at 373 K, were thoroughly characterized using XRD, TEM-SAED, N-2 adsorption, XPS, UV-vis diffuse reflectance, and photoluminescence spectroscopy. These hybrids were applied as photoelectrochemical (PEC) materials for water splitting and as photocatalysts for methylene blue (MB) degradation under visible light irradiation. GO(1) :Mn-1 has indicated higher PEC activity towards water splitting with supreme photocurrent density (0.875 mA cm(-2)) doubling that of GO(5):Mn-1 (0.350 mA cm(-2)). High optical absorption and charge transfer rate played key roles in enhancing the PEC activity of the former comparatively; as recorded via chronoamperometric curves. Concurrently, the incident photon to current efficiency (IPCE) of GO(1) :Mn-1 has exceeded the rest of hybrids in the wavelength range of 500-850 nm. Increasing the dispersion of MnFe2O4 between G/GO sheets in GO(1):Mn-1 lowering the E-g (0.55 eV) value, increasing reduced graphene ratio over oxidized ones as well as increasing the pore radius (76.5 angstrom) value has all shared in increasing the photocurrent density. More specifically, the residual oxides depicted in GO(1):Mn-1 (9%); as calculated via XPS, were important in evoking the reactive intermediates center dot OH and center dot O-2(-); those were responsible for the MB degradation. Increasing the ratio of the reduced graphene (91%) in this particular sample (GO(1):Mn-1) was chiefly important for lowering the energy gap (E-g) value. In agreement, impedance spectroscopy of the GO(1) :Mn-1 sample has substantiated the charger transfer process; depicted from optical results, via exhibiting the lowest resistance between all the nanohybirds. This latter hybrid of nano-spindle shape and monomodal mesopore type of pores (140 angstrom) has presented high photocatalytic degradation for MB (10 ppm, 1 g/L, 30 min) with rate constant 0.037 min(-1) surpassing the rest of samples. (C) 2016 Elsevier B.V. All rights reserved.