Removing Cr (VI) in water via visible-light photocatalytic reduction over Cr-doped SrTiO3 nanoplates

Transient Photocurrent Responses of Sr1-xCexTiO3 Perovskites Under Visible Light Illumination for Photovoltaic Applications

The objective of this study was to synthesize strontium titanate (Sr1-xCexTiO3) doped with Ce3+ by solid state method. Its crystalline structure is Sr1-xCexTiO3, and its bandgap ranges from ~3.3 to ~2.7 eV. In the photoluminescence of samples excited at 288 nm, the maximum emission of blue light was observed at 380 and 390 nm. Photocatalytic results show that dye molecules have a high absorbance, whereas their surface area is large. According to a line sweep voltammetric plot (LSV), illumination increases the current density by 0.4 μA cm-2 compared with dark conditions. It was demonstrated that the material changed from n-type to p-type under doping. Chronoamperometry spectra were obtained for sample Sr1-xCexTiO3 (x = 0, 0.005, 0.01, 0.03, 0.05) when an electrical voltage of 0.8 V was applied versus NHE. The plots indicate an increase in the current density under "light ON" conditions and a decrease under "light OFF" conditions. As Ce3+ concentration increases, the photocurrent increases until about 3 mol%, after which it decreases abruptly.

The Emerging Career of Strontium Titanates in Photocatalytic Applications: A Review

The growing energy demands and rapid industrialization drove the attention towards a sustainable living. The methods to a adopt renewable source of energy has made the field of heterogeneous photocatalysis so famous. The photocatalytic hydrogen production seems to be an answer for our future energy crisis. In this regard, alkaline earth metal titanates with a perovskite structure are one of the in demand materials these days. Among these, strontium titanates (SrTiO3) play an important role and have shown a potential, especially in the field of hydrogen production. This review summarizes the significance of (SrTiO3) in photocatalytic water splitting, to produce hydrogen and the photocatalytic degradation of the pollutants from the waste water. Different synthesis methods used for preparing SrTiO3 are also discussed.

Cu2O/SrTi1-xCrxO3 Heterojunction Photocatalyst for the Efficient Degradation of Isopropanol under Visible Light Irradiation

A heterojunction of Cu₂O and Cr-doped SrTiO₃ (SrTi_1-xCr_xO₃) was designed for selective photocatalytic isopropanol (IPA) oxidation under visible light irradiation. The photocatalytic oxidation of IPA was measured in a fixed-bed reactor. Cr dopants can increase the light absorption and improve the activity of the catalyst. The formation of the Cu₂O/SrTi_1-xCr_xO₃ heterojunction can further broaden the absorption range of lights and dramatically increase the photocatalytic activity for selective oxidation of IPA. The 3% Cu₂O/SrTi_0.99Cr_0.01O₃ catalyst can fully convert ∼1000 ppm IPA under illumination in 2 h. The selectivity of acetone is ∼100%. The yield is 83 and 4 times higher than that using SrTiO₃ and SrTi_0.99Cr_0.01O₃ as catalysts, respectively. By measuring the ultraviolet-visible absorption spectra and Mott-Schottky plots, we obtained the band structure of the heterojunction, which shows that the conduction and valence bands of Cu₂O are higher than those of SrTi_1-xCr_xO₃, therefore facilitating the separation and transfer of photogenerated electrons and holes. In addition, electron paramagnetic resonance spectroscopy and radical trapping tests reveal that the generation of hydroxyl and superoxide leads to photocatalytic oxidation of IPA by the heterojunction photocatalyst.

Process enhancing strategies for the reduction of Cr(VI) to Cr(III) via photocatalytic pathway

This discourse aimed at providing insight into the strategies that can be adopted to boost the process of photoreduction of Cr(VI) to Cr(III). Cr(VI) is amongst the highly detestable pollutants; thus, its removal or reduction to an innocuous and more tolerable Cr(III) has been the focus. The high promise of photocatalysis hinged on the sustainability, low cost, simplicity, and zero sludge generation. Consequently, the present dissertation provided a comprehensive review of the process enhancement procedures that have been reported for the photoreduction of Cr(VI) to Cr(III). Premised on the findings from experimental studies on Cr(VI) reductions, the factors that enhanced the process were identified, dilated, and interrogated. While the salient reaction conditions for the process optimization include the degree of ionization of reacting medium, available photogenerated electrons, reactor ambience, type of semiconductors, surface area of semiconductor, hole scavengers, quantum efficiency, and competing reactions, the relevant process variables are photocatalyst dosage, initial Cr(VI) concentration, interfering ion, and organic load. In addition, the practicability of photoreduction of Cr(VI) to Cr(III) was explored according to the potential for photocatalyst recovery, reactivation, and reuse reaction conditions and the process variables.

Engineered magnetic oxides nanoparticles as efficient sorbents for wastewater remediation: a review

The rapid urbanization and industrialization is causing worldwide water pollution, calling for advanced cleaning methods. For instance, pollutant adsorption on magnetic oxides is efficient and very practical due to the easy separation from solutions by an magnetic field. Here we review the synthesis and performance of magnetic oxides such as iron oxides, spinel ferrites, and perovskite oxides for water remediation. We present structural, optical, and magnetic properties. Magnetic oxides are also promising photocatalysts for the degradation of organic pollutants. Antimicrobial activities and adsorption of heavy metals and radionucleides are also discussed.

Manipulating the Structure and Characterization of Sr1−xLaxTiO3 Nanocubes toward the Photodegradation of 2-Naphthol under Artificial Solar Light

Effective La-doped SrTiO3 (Sr1−xLaxTiO3, x = 0–0.1 mol.% La-doped) nanocubes were successfully synthesized by a hydrothermal method. The influence of different La dopant concentrations on the physicochemical properties of the host structure of SrTiO3 was fully characterized. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed that the Sr2+ in the crystal lattice of SrTiO3 was substituted by La3+. As a result, the absorption region of the Sr1−xLaxTiO3 could be extended to visible light. Scanning electron microscopy (SEM) images confirmed that their morphologies are associated with an increased surface area and an increased La-doping concentration. The decrease in the photoluminescence (PL) intensity of the dopant samples showed more defect levels created by the dopant La+3 cations in the SrTiO3 structure. The photocatalytic activities of Sr1−xLaxTiO3 were evaluated with regard to the degradation of 2-naphthol at typical conditions under artificial solar light. Among the candidates, Sr0.95La0.05TiO3 exhibited the highest photocatalytic performance for the degradation of 2-naphthol, which reached 92% degradation efficiency, corresponding to a 0.0196 min−1 degradation rate constant, within 180 minutes of irradiation. Manipulating the structure of Sr1−xLaxTiO3 nanocubes could produce a more effective and stable degradation efficiency than their parent compound, SrTiO3. The parameters remarkably influence the Sr1−xLaxTiO3 nanocubes’ structure, and their degradation efficiencies were also studied. Undoubtedly, substantial breakthroughs of Sr1−xLaxTiO3 nanocube photocatalysts toward the treatment of organic contaminants from industrial wastewater are expected shortly.

Green and controllable synthesis of one-dimensional Bi2O3/BiOI heterojunction for highly efficient visible-light-driven photocatalytic reduction of Cr(VI)

BiOI nanosheets have been successfully deposited on the porous Bi₂O₃ nanorobs via a one-pot precipitation method. The physicochemical features of the as-prepared materials were characterized in detail by a series of techniques, and the results revealed that BiOI nanosheets were evenly distributed on the porous Bi₂O₃ nanorobs. Because of higher photogenerated electron-hole pairs separation efficiency and the larger specific surface area compared to the pristine Bi₂O₃ and BiOI, the 50%Bi₂O₃/BiOI composite exhibited significantly enhanced photocatalytic activity for Cr(VI) reduction under visible light irradiation, and the reduction rate constant was 0.02002 min^-1, which was about 27.4 and 2.6 times higher than that of pure Bi₂O₃ (0.00073 min^-1) and BiOI (0.00769 min^-1), respectively. Moreover, the 50%Bi₂O₃/BiOI composite also possessed the excellent photochemical stability and recyclability, thereby facilitating its wastewater treatment application.

A review on the preparation, characterization and potential application of perovskites as adsorbents for wastewater treatment

Perovskite are among the popular materials utilized in many areas of modern industrialization because of their low price, high stability, excellent oxidation activity, adsorptive, catalytic, optical, magnetic, electronic and ferroelectric properties. Over the years, widespread usage of perovskite nanoparticles has been reported due to its various applications which include an environmental catalyst, fuel cells, chemical sensors, magnetic materials, oxygen permeable membranes and adsorbents for wastewater treatment. Various synthetic methods such as the sol-gel method, proteic method, Pechini method, combustion, co-precipitation, and chelating precursor method have been applied in producing perovskites. Therefore, this review assembles the current knowledge on the processes involved in the preparation of perovskites, their characterizations and potential applications in wastewater treatment. Challenges and future opportunities of perovskite-based materials are discussed as well as obstacles against their extensive uses. Conclusions have also been drawn proposing a few suggestions for future research.

Synergistic Effect of Hydrochloric Acid and Phytic Acid Doping on Polyaniline-Coupled g-C3N4 Nanosheets for Photocatalytic Cr(VI) Reduction and Dye Degradation

In this study, graphitic carbon nitride (g-C₃N₄) nanosheets (CNns) were modified using polyaniline (PANI) codoped with an inorganic (hydrochloric acid, HCl) and an organic (phytic acid, PA) acid. Our results revealed that these samples exhibited extended visible-light absorption and a three-dimensional (3D) hierarchical structure with a large specific surface area. They also inhibited photoluminescence emission, reduced electrical resistance, and provided abundant free radicals, resulting in high photocatalytic performance. The PANI/g-C₃N₄ sample demonstrated outstanding photocatalytic activity of a Cr(VI) removal capacity of 4.76 mg·min^-1·g_c^-1, which is the best record for the reduction of a 100 ppm K₂Cr₂O₇ solution. Moreover, g-C₃N₄ coupled with PANI monotonically doped with HCl or PA did not demonstrate increased activity, suggesting that the codoping of HCl and PA plays a significant role in enhancing the performance. The improved photocatalytic activity of PANI/g-C₃N₄ can be attributed to the interchain and intrachain doping of PA and HCl over PANI, respectively, to create a 3D connected network and synergistically increase the electrical conductivity. Therefore, new insights into g-C₃N₄ coupled with PANI and codoped by HCl and PA may have excellent potential for the design of g-C₃N₄-based compounds for efficient photocatalytic reactions.

Powerful combination of g-C3N4 and LDHs for enhanced photocatalytic performance: A review of strategy, synthesis, and applications

The utilization of solar energy with photocatalytic technology has been considered a good solution to alleviate environmental pollution and energy shortage. Constructing 2D/2D heterostructure photocatalysts with layered double hydroxide (LDH) and graphitic carbon nitride (g-C₃N₄) is an effective approach to attain high performance in solar photocatalysis. This paper provides a review of recent studies about 2D/2D LDH/g-C₃N₄ heterostructure photocatalysts. Main strategies for constructing the desired 2D/2D heterojunction are summarized. The planar structure of LDH and g-C₃N₄ offers a shorter transfer distance for charge carriers and reduces electron-hole recombination in the bulk phase. The face-to-face contact between the two materials can promote the charge transfer across the heterostructure interface, thus improving the electron-hole separation efficiency. The performance and mechanisms of LDH/g-C₃N₄ photocatalysts in hydrogen production, CO₂ reduction, and organic pollutant degradation are analyzed and discussed. Incorporating reduced graphene oxide or Ag nanoparticles into LDH/g-C₃N₄ heterojunction and fabricating calcined LDH/g-C₃N₄ composites are effective strategies to further facilitate charge transfer at the interface of LDH and g-C₃N₄ and improve the absorption capacity for visible light. This review is expected to provide basic insights into the design of 2D/2D LDH/g-C₃N₄ heterojunctions and their applications in solar photocatalysis.

Boosting charge separation of Sr2Ta2O7 by Cr doping for enhanced visible light-driven photocatalytic hydrogen generation

Visible-light driven Cr-doped Sr₂Ta₂O₇ nanosheets with enhanced photocatalytic performance were prepared by a facile hydrothermal method.