Abstract:The low-toxicity treatment of chromium-containing wastewater represents an important way of addressing key environmental problems. In this study, a core-shell structural ZIF-8@TiO2 photocatalyst was synthesized by a simple one-step hydrothermal method. The obtained composite photocatalyst possessed improved photocatalytic activity compared with TiO2. The results indicated that the optimized ZIF-8@TiO2 composite exhibited the highest removal efficiency with 93.1% of Cr(VI) after 120 min under UV-vis irradiation… Show more
“…The percentages of Cr(VI) and Fe(III) removal were 70 and 63%, respectively, after 360 min. These values were consistent with those reported in the literature for these ions [ [68] , [69] , [70] ]. Fig.…”
“…The percentages of Cr(VI) and Fe(III) removal were 70 and 63%, respectively, after 360 min. These values were consistent with those reported in the literature for these ions [ [68] , [69] , [70] ]. Fig.…”
“…As previously explained, TiO2 has an abundant number of hydroxyl group compounds on its surface. In acidic conditions, many positive charges are generated on the surface of TiO2 [29]. As shown in Figure 8, elevated concentrations of TiO2 and hydroxyl groups are generated, leading to an intensified electrostatic interaction with Cr(VI).…”
This research explores the adsorption effectiveness of NiZnFe2O4/TiO2 nanocomposites regarding Cr(VI). The nanocomposites were effectively synthesized utilizing coprecipitation and Stöber methods, incorporating diverse molar ratios of TiO2. The samples were subjected to characterization using methods such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), Fourier-transform infrared (FTIR), vibrating sample magnetometer (VSM), and ultraviolet-visible spectroscopy (UV-Vis). These analyses were conducted to evaluate the crystal structure, morphology, chemical bond formation, optical properties, magnetic properties, and removal efficiency of the specimens. XRD results showed that NiZnFe2O4 and TiO2 have a cubic and tetragonal structure. The crystallite size decreased as the TiO2 concentration increased. TEM image of NiZnFe2O4 reveals the formation of clusters, indicating uneven dispersion under agglomerated conditions. The average particle size is measured at (10.6 ± 0.8) nm. The Fourier-transform infrared (FTIR) analysis demonstrated the presence of functional groups O-H, C-H, and H-O-H, indicating the successful synthesis of the material. Moreover, the identification of MO-octahedral, MO-tetrahedral, and Ti-O functional groups suggested the formation of NiZnFe2O4/TiO2 nanocomposites. The incorporation of TiO2 had an impact on both the saturation magnetization and coercivity values, which fell within the ranges of 12.4 to 22.9 emu/g and 47 to 55 Oe, respectively. This finding indicates the presence of advantageous magnetic properties. The absorbance spectrum of these nanocomposites displayed a shift to the right (redshift), allowing them to absorb ultraviolet rays. The band gap of these nanocomposites ranges from (2.85 ± 0.02) to (3.29 ± 0.02) eV. Notably, NiZnFe2O4/TiO2 nanocomposites with a concentration ratio of 1:5 exhibit effective Cr(VI) removal efficiency, achieving a degradation value of 65.6%. The pseudo-kinetic model was first investigated to describe kinetic data and Cr(VI) removal determination. The SEM-EDX adsorbent results after adsorption showed the presence of Cr(VI) in the nanocomposites. Therefore, these results can promote NiZnFe2O4/TiO2 nanocomposites as a promising candidate in the removal of heavy metal waste.
“…As illustrated in Figure 4a, when the Cr(VI) concentration gradually increases from 0.08 µM to 80 µM, the overall photocurrent at the same measuring time steadily decreases. The corresponding Cr 2p XPS peak in Figure 4b could be fitted into two main peaks: the one located at lower binding energy (573.1 eV) corresponds to Cr(III), and the other peak centered at higher binding energy (575.4 eV) originates from Cr(VI) [34,35]. It is obvious that the area ratio of the Cr(III) sub-peak to the total peak for the sample being tested in the higher-concentration Cr(VI) is larger than that in the lower-concentration Cr(VI), confirming the presence of more Cr(III) in the photocathode surface for the Cr(VI) solution with a higher concentration.…”
Photoelectrochemical (PEC) sensors show great potential for the detection of heavy metal ions because of their low background noise, high sensitivity, and ease of integration. However, the detection limit is relatively high for hexavalent chromium (Cr(VI)) monitoring in addition to the requirement of an external bias. Herein, a CuO film is readily synthesized as the photoactive material via reactive sputtering and thermal annealing in the construction of a PEC sensing photocathode for Cr(VI) monitoring. A different mechanism (i.e., Signal-Weakening PEC sensing) is confirmed by examining the electrochemical impedance and photocurrent response of different CuO film photoelectrodes prepared with the same conditions in contact with various solutions containing concentration-varying Cr(VI) for different durations. The detection of Cr(VI) is successfully achieved with the Signal-Weakening PEC response; a drop of photocathode signal with an increasing Cr(VI) concentration from the steric hindrance effect of the in situ formed Cr(OH)3 precipitates. The photocurrent of the optimized CuO film photocathode linearly declines as the concentration of Cr(VI) increases from 0.08 to 20 µM, with a detection limit down to 2.8 nM (Signal/Noise = 3) and a fitted sensitivity of 4.22 µA·μM−1. Moreover, this proposed sensing route shows operation simplicity, satisfactory selectivity, and reproducibility.
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