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Hexavalent chromium (Cr(VI)) is carcinogenic to organisms. It is widely used in several industries. In this work, we investigated the Cr(VI) photocatalytic reaction with a scavenger on Pt and Cu-TiO2 photocatalysts. Metal-deposited TiO2 was successfully synthesized by a photodeposition method. TEM-EDX, XRD, and UV-DR were analyzed to study the changes in morphology, crystallinity, and the electronic properties of photocatalysts. The rate of charge recombination during reduction and photoluminescence (PL) spectroscopy was used to examine the catalysts in depth. Cu-TiO2 demonstrates the highest photocatalytic activity for 63.74% of Cr(VI) removal. To understand the photoreduction of Cr(VI), the fate transformation of Cr species during the adsorption and reaction was investigated using in situ XANES. The results demonstrated that the Cr(III) was noticeably main component adsorbed over the catalyst, particularly in Cu˗TiO2. The presence of humic acid can boost the Cr(VI) removal efficiency and enhanced the Cr(VI) reduction to Cr(III). We believe that the extensive research on Cr(VI) photoreduction on metal-TiO2 heterojunction will provide a comprehensive understanding of catalytic behaviors, paving the way for rationally designed novel Cr reduction catalysts. [ABSTRACT FROM AUTHOR]

The removal of selenate (Se6+) from aqueous solutions by zeolite Na-P1 supported nanoscale zero-valent iron (Z-NZVI) was investigated. Zeolite was synthesized from the fly ash of the byproducts discharged from coal-fired power, and used as supporting material for NZVI. The synthesized Z-NZVI was characterized using various techniques including x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and BET surface area analysis, and. The results revealed that iron nanoparticles were highly dispersed on the zeolite surfaces which apparently lessened the agglomeration of iron nanoparticles resulting in the enhanced reduction process. The adsorption of Se6+ on Z-NZVI related well with Langmuir isotherm model with maximum adsorption capacity of 15.432 mg·g-1. The experimental results showed that the removal of Se6+ by Z-NZVI increased when the temperature increased. The reactions were found to conform to pseudo second order kinetics. The reaction process occurred spontaneously (-ΔG°), in an endothermic process (ΔH°=29.6 J·mol-1), and with increased randomness (ΔS°=97.17 J·mol-1K-1). This study suggested that ZNZVI is a promising and efficient material for the selenate removal from wastewater. [ABSTRACT FROM AUTHOR]

This work aims to enhance the value of palm empty fruit bunches (EFBs), an abundant residue from the palm oil industry, as a precursor for the synthesis of luminescent carbon dots (CDs). The mechanism of fIuorimetric sensing using carbon dots for either enhancing or quenching photoluminescence properties when binding with analytes is useful for the detection of ultra-low amounts of analytes. This study revealed that EFB-derived CDs via hydrothermal synthesis exceptionally exhibited luminescence properties. In addition, surface modification for specific binding to a target molecule substantially augmented their PL characteristics. Among the different nitrogen and sulfur (N and S) doping agents used, including urea (U), sulfate (S), p-phenylenediamine (P), and sodium thiosulfate (TS), the results showed that PTS-CDs from the co-doping of p-phenylenediamine and sodium thiosulfate exhibited the highest PL properties. From this study on the fluorimetric sensing of several metal ions, PTS-CDs could effectively detect Fe3+ with the highest selectivity by fluorescence quenching to 79.1% at a limit of detection (LOD) of 0.1 µmol L−1. The PL quenching of PTS-CDs was linearly correlated with the wide range of Fe3+ concentration, ranging from 5 to 400 µmol L−1 (R2 = 0.9933). [ABSTRACT FROM AUTHOR]

Box-Behnken design (BBD) was employed to study an optimal treatment method of synthetic lignin wastewater effluent from pulp and paper wastewater treatment plants using iron (III) trimesate (Fe-BTC) as an alternative coagulant aid. Fe-BTC was prepared by hydrothermal technique using ferric chloride hexahydrate (FeCl3·6H2O) combined with 1,3,5-benzenetricarboxylic acid (trimesic acid, H3BTC) in deionized water and ethanol. X-ray diffractometry and Fourier transform infrared spectroscopy were used to characterize the property of Fe-BTC. Three quadratic models of the four factors including Fe-BTC dosage, pH, initial lignin concentration, and slow mixing time were defined with lignin removal efficiency as a response. Treatment efficiency of lignin removal was 50-80% for experimental data and 60-80% for predicted values. Optimal condition was 1 g/L of Fe-BTC dosage, pH 4, and 50 ppm of initial lignin concentration without slow mixing giving 58.34% lignin removal efficiency. The pH of treated samples was below 3 after all processes. Results showed that Fe-BTC enhanced separation of lignin by coagulation-flocculation. Adsorption-charge neutralization is the main mechanism of this process at acidic pH. Fe-BTC separated the wastewater into three layers with Fe-BTC powder at the bottom, lignin sludge in the middle, and clear supernatant at the top. Lignin sludge can be reused and recycled for use in other applications. [ABSTRACT FROM AUTHOR]

Sugarcane bagasse ash (SCBA) is a solid waste containing a high amount of silica (SiO 2 ) and is suitable to utilize as a silica source for synthesizing zeolite NaA. SCBA is typically calcined at high temperatures before silica extraction. The method is not environmentally friendly because it consumes energy and produces CO 2 . This work demonstrates an alternative extraction method of SiO 2 from SCBA by treating it with hydrochloric (HCl) and sodium hydroxide (NaOH) solution. The obtained mixture was separated by paper filter No. 1 (P) and a combination of paper filter and syringe filter (PS). The solution was neutralized by HCl solution, producing silica (SiO 2 -P and SiO 2 -PS) with a purity of 98 wt%. Both SiO 2 samples and SCBA were utilized to synthesize zeolite NaA for CO 2 adsorption. The CO 2 adsorption capacities of NaA-P and NaA-PS were 4.30 and 4.10 mmol g adsorbent -1 , in the same range as commercial NaA. The capacity is influenced by the total basicity of zeolite. The CO 2 adsorption behavior of all samples correlates well with the Toth model. The CO 2 adsorption kinetics agrees well with the pseudo-second-order kinetic model. Overall, this work shows the successful extraction of silica via using a direct NaOH solution, yielding high-purity silica sufficient for synthesizing zeolite NaA, a promising adsorbent of CO 2 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Hexavalent chromium (Cr(VI)) is carcinogenic to organisms. It is widely used in several industries. In this work, we investigated the Cr(VI) photocatalytic reaction with a scavenger on Pt and Cu-TiO 2 photocatalysts. Metal-deposited TiO 2 was successfully synthesized by a photodeposition method. TEM-EDX, XRD, and UV-DR were analyzed to study the changes in morphology, crystallinity, and the electronic properties of photocatalysts. The rate of charge recombination during reduction and photoluminescence (PL) spectroscopy was used to examine the catalysts in depth. Cu-TiO 2 demonstrates the highest photocatalytic activity for 63.74% of Cr(VI) removal. To understand the photoreduction of Cr(VI), the fate transformation of Cr species during the adsorption and reaction was investigated using in situ XANES. The results demonstrated that the Cr(III) was noticeably main component adsorbed over the catalyst, particularly in Cu-TiO 2 . The presence of humic acid can boost the Cr(VI) removal efficiency and enhanced the Cr(VI) reduction to Cr(III). We believe that the extensive research on Cr(VI) photoreduction on metal-TiO 2 heterojunction will provide a comprehensive understanding of catalytic behaviors, paving the way for rationally designed novel Cr reduction catalysts., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)