Facile Synthesis of Cu-Zn Binary Oxide Coupled Cadmium Tungstate (Cu-ZnBO-Cp-CT) with Enhanced Performance of Dye Adsorption

This study reports the synthesis of copper–zinc binary oxide coupled cadmium tungstate through a simple bio-precipitation method followed by calcination at 600 °C and its adsorption application. The characterization analysis reveals that the prepared composite has low particles size (nano-range), high porosity, and functional groups on the surface. The calcination of sample at 600 °C causes some essential function groups to disappear on the surface. Prepared composite was found to be effective adsorptive material to treat Congo red dye in aqueous solution. 2.5 g L−1 dose of adsorbent could remove more than 99% Congo red dye from 10 mg L−1 solution and more than 80% Congo red dye from 60 mg L−1 aqueous solution. The maximum adsorption capacity of present adsorbent was calculated to be 19.6 mg Congo red per gram of adsorbent. Isotherms analysis suggested a physio-chemical adsorption process. Thermodynamic analysis revealed a exothermic and feasible adsorption process. Adsorption rate was well explained by pseudo second order kinetics. The rate determining step was intra-particle diffusion evaluated from the Weber-Morris plot. To assess the adsorption performance of present adsorbent for Congo red dye the partition coefficient and adsorption equilibrium capacity were compared with other adsorbents. The partition coefficient and adsorption equilibrium values for 10 mg L−1 aqueous solution were found to be approximately 83.3 mg g−1 µM−1 and 4.0 mg g−1 at 30 °C and 7.0 pH using 2.5 g L−1 adsorbent. The value of partition coefficient was found to be higher than previous reported zinc oxide coupled cadmium tungstate having partition coefficient = as 21.4 mg g−1 µM−1 at 30 °C and 7.0 pH using 2.0 g L−1 adsorbent (Fatima, B.; Siddiqui, S.I.; Nirala, R.K. et al., Environ. Poll. 2021, 271, 116401). These results suggested that present adsorption technology is efficient for wastewater treatment.

Synthesis, Optical Characterization, and Adsorption of Novel Hexavalent Chromium and Total Chromium Sorbent: A Fabrication of Mulberry Stem Biochar/Mn-Fe Binary Oxide Composite via Response Surface Methodology

In this study, a new generation chromium sorbent, mulberry stem biochar/Mn-Fe binary oxide composite (MBC-MFC), was fabricated by chemical precipitation on carbonized mulberry stem according to response surface methodology (RSM) results. RSM was more convenient to figure out the optimized preparation condition of MBC-MFC theoretically for achieving a maximum removal efficiency of Cr(VI) and total chromium (TCr), compared to labor-intensive orthogonal experiments. The RSM results showed that Fe/Mn concentration (CFe; CMn), MBC activation temperature after soaking in KOH solution (T), and pH during precipitation of Fe-Mn oxide were three main factors to significantly affect the efficiency of MBC-MFC (p < 0.05) in Cr(VI) and TCr removal. With the selected condition (CFe = 0.28 mol/L; CMn = 0.14 mol/L; T = 790°C; pH = 9.0), MBC-MFC was synthesized with a large surface area (318.53 m2/g), and the point of zero charge values of MBC-MFC was 5.64. The fabricated MBC-MFC showed excellent adsorption performance of Cr(VI) and TCr in an aqueous solution. The maximum Cr(VI) and TCr removal capacity of MBC-MFC was 56.18 and 54.97 mg/g (T = 25°C, pH = 3.0, t = 48 h, and dosage = 0.10 g/50 ml), respectively, and the maximum Cr(VI) adsorption of MBC-MFC was 4.16 times that of bare MBC, suggesting the synergistic effects of Fe/Mn oxides and MB on the performance of MBC-MFC in Cr(VI) and TCr removal. The adsorption mechanism of MBC-MFC on chromium was mainly contributed by surface complexation and electrostatic attraction. Our study offers valuable outlooks to develop high-performance biochar-based sorbents for heavy metal removal and sustainable environmental remediation.