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The growing needs of the rising population and blatant misuse of resources have contributed enormously to environmental problems. Among the various methods, photocatalysis has emerged as one of the effective remediation methods. The continuous search for effective photocatalysts that can be made from abundant, cheap, non-toxic materials is going on. Although sulfur is a known insulator, recent sulfur use as a visible light photocatalyst has ushered a new era in this direction. Sulfur is a non-toxic, cheap, and abundant photocatalyst, exhibiting significant photocatalytic properties. But, hydrophobicity, poor light-harvesting and high recombination rate of charge carriers in elemental sulfur photocatalyst are some of the major drawbacks of the elemental sulfur photocatalyst. The photocatalytic activity of sulfur as a single element was low, but various methods such as nanoscaling, heterojunction formation, doping and surface modifications have been used to enhance it. The review highlights sulfur's crystal structure, electronic and optical properties, and morphological changes, making it an excellent visible light photocatalyst. The article points to the limitations of sulfur as a single photocatalyst and various strategies to improve the shortcomings. More recently, there has been an emphasis on the synthesis of metal-free photocatalysts. This review provides its readers with a comprehensive detail of sulfur being used as a dopant in improving the photocatalytic properties of metal-free photocatalysts and their environmental remediation use. Finally, the conclusion and future perspectives for sulfur-based nanostructures are presented.

Herein, we report synthesis of graphitic carbon sand composite (GSC) and bentonite (BT) supported superparamagnetic MnFe2O4 nanoparticles to obtain MnFe2O4/GSC and MnFe2O4/BT nanocomposites. Graphitic carbon sand composite (GSC) was prepared by graphitization of sugar over river sand. The particle size of MnFe2O4/GSC and MnFe2O4/BT was found to be 50 and 60 nm respectively. BET adsorption experiments confirmed mesoporous nature of prepared photocatalysts. Magnetic studies revealed superparamagnetic behavior of MnFe2O4/GSC and MnFe2O4/BT. The band gaps of MnFe2O4/GSC and MnFe2O4/BT were 2.38 and 2.42 eV respectively. Both MnFe2O4/GSC and MnFe2O4/BT exhibited significant photocatalytic activity for the mineralization of ampicillin (AMP) and oxytetracycline (OTC) antibiotics under solar light. Simultaneous adsorption and degradation process (A + P) resulted in higher photodegradation of OTC and AMP. The applicability of power law model indicated intricacies of mineralization process. MnFe2O4/GSC and MnFe2O4/BT displayed significant recycle efficiency and easier recovery of photocatalyst for 10 consecutive catalytic cycles.

Adsorbent supported photocatalysis is developing as a potential waste water treatment technology. In this work, NiFe 2 O 4 was supported onto graphene sand composite (GSC) and bentonite (BT) supported to prepare magnetic NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT nanocomposties. Graphene sand composite (GSC) was prepared by graphitization of sugar over river sand. The size of NiFe 2 O 4 /BT and NiFe 2 O 4 /GSC was found to be 50 and 60 nm respectively. Mesoporous nature of prepared photocatalysts was confirmed by BET adsorption/desorption experiments. NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT exhibited ferromagnetic behaviour and could be separated from treated water using external magnetic field. The band gaps of NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT were found to be 2.41 and 2.42 eV, respectively. The adsorption and photocatalytic activity of NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT was tested for the mineralization of ampicillin (AMP) and oxytetracycline (OTC) antibiotics under solar light. The adsorption process had significant effect on the mineralization of AMP and OTC. Simultaneous adsorption and degradation (A + P) process were the most efficient for antibiotic degradation. The complete mineralization of antibiotics was obtained using NiFe 2 O 4 /GSC/A + P and NiFe 2 O 4 /BT/A + P catalytic processes. The kinetics of mineralization were explored using power law model. Magnetically recoverable NiFe 2 O 4 /GSC and NiFe 2 O 4 /BT are recyclable and displayed significant recycle efficiency and quick recovery for 10 consecutive catalytic cycles.

The study investigates photocatalytic activity of hydroxyapatite supported BiOCl (BiOCl/HA) in the presence of H2O2. BiOCl/HA was prepared by simple hydrolysis method. BiOCl/HA was characterized using scanning electron microscopy (SEM), tunneling electron microscopy (TEM), Xray diffraction (XRD), energy diffraction X-ray (EDX), Fourier transform infrared spectroscopy (FTIR) and UV-visible (UV-vis)analysis. SEM results confirmed the dispersion of BiOCl onto hydroxyapatite. BiOCl/HA exhibited irregular pleats-like structure having average size of 80 nm. The band gap of BiOCl/HA was found to be 3.42 eV. The solar light was used as radiation source during photocatalysis. Both H2O2 and BiOCl/HA had synergistic effect on oxytetracycline removal. The simultaneous adsorption and photocatalysis (A+P) was most efficient process for OTC removal. The photocatalytic degradation of oxytetracycline obeyed pseudo first order kinetics. The effect of process parameters catalyst loading, H2O2 concentration, pH and OTC concentration was investigated on photocatalysis. The oxidative removal occurred through hydroxyl radical formation. BiOCl exhibited significant recycle efficiency due to easier separation and stability in reaction solution. Solar/H2O2/BiOCl/HA displayed excellent photocatalytic property for degradation of OTC from aqueous solution. Copyright © 2016 VBRI Press.