Facile Synthesis of Novel CaIn(2)S(4)/ZnIn(2)S(4) Composites with Efficient Performance for Photocatalytic Reduction of Cr(VI) under Simulated Sunlight Irradiation

A series of novel and efficient heterostructured composites CaIn(2)S(4)/ZnIn(2)S(4) have been synthesized using a facile hydrothermal method. XRD patterns indicate the as-prepared catalysts are two-phase composites of cubic phase CaIn(2)S(4) and hexagonal phase ZnIn(2)S(4). FESEM (field emission scanning electron microscope) images display that the synthesized composites are composed of flower-like microspheres with wide diameter distribution. UV–Vis diffuse reflectance spectra (DRS) show that the optical absorption edges of the CaIn(2)S(4)/ZnIn(2)S(4) composites shift toward longer wavelengths with the increase of the CaIn(2)S(4) component. The photocatalytic activities of the as-synthesized composites are investigated by using the aqueous-phase Cr(VI) reduction under simulated sunlight irradiation. This is the first report on the application of the CaIn(2)S(4)/ZnIn(2)S(4) composites as stable and efficient photocatalysts for the Cr(VI) reduction. The fabricated CaIn(2)S(4)/ZnIn(2)S(4) composites possess higher photocatalytic performance in comparison with pristine CaIn(2)S(4) or ZnIn(2)S(4). The CaIn(2)S(4)/ZnIn(2)S(4) composite with a CaIn(2)S(4) molar content of 30% exhibits the optimum photocatalytic activity. The primary reason for the significantly enhanced photoreduction activity is proved to be the substantially improved separation efficiency of photogenerated electrons/holes caused by forming the CaIn(2)S(4)/ZnIn(2)S(4) heterostructured composites. The efficient charge separation can be evidenced by steady-state photoluminescence spectra (PLs) and transient photocurrent response. Based on the charge transfer between CaIn(2)S(4) and ZnIn(2)S(4), an enhancement mechanism of photocatalytic activity and stability for the Cr(VI) reduction is proposed.