Hussaini Minaam, Vohra Muhammad
Civil and Environmental Engineering Department, King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia.
Interdisciplinary Research Center for Construction and Building Materials (IRC-CBM), King Fahd University of Petroleum & Minerals (KFUPM), Dhahran 31261, Saudi Arabia.
Nanomaterials (Basel). 2022 Jun 14;12(12):2035. doi: 10.3390/nano12122035.
Selenium as a nutrient has a narrow margin between safe and toxic limits. Hence, wastewater discharges from selenium-containing sources require appropriate treatment that considers health concerns and stringent selenium-related water treatment standards. This work examined the use of a photocatalysis-cum-adsorption system based on a layered double hydroxide coupled with TiO2 (LDH-TiO2) to remove aqueous phase selenocyanate (SeCN−), which is difficult to treat and requires specific treatment procedures. The synthesized LDH and LDH-TiO2 composite samples were characterized using the X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and thermogravimetry analysis (TGA) methods. The XRD results for the uncalcined LDH indicated a hydrotalcite mass with a rhombohedral structure, whereas increasing the calcination temperature indicated transition to an amorphous state. FESEM results for the LDH-TiO2 matrix indicated round titanium dioxide particles and LDH hexagonal layers. The TGA findings for uncalcined LDH showed a gradual decrease in weight up to 250 °C, followed by a short plateau and then a sharp decrease in LDH weight from 320 °C, with a net weight loss around 47%. Based on the characterization and initial selenocyanate adsorption results, the 250 °C calcined LDH-TiO2 matrix was used for the selenocyanate photocatalysis. A ~100% selenium removal was observed using LDH:TiO2 at a 1.5:1 w/w ratio with a 2 g/L dose, whereas up to 80% selenium removal was noted for LDH:TiO2 at a 0.5:1 w/w ratio. The respective difference in the efficiency of selenium treatment was attributed to enhanced LDH-based adsorption sites in the enhanced LDH:TiO2 w/w ratio. Furthermore, the selenite and selenate that occurred during SeCN− photocatalytic degradation (PCD) were also nearly completely removed via adsorption. An optimization exercise using response surface methodology (RSM) for total selenium removal showed R2 values of more than 0.95, with a prediction accuracy of more than 90%. In summary, the present findings show that the use of a photocatalysis-cum-adsorption system based on LDH-TiO2 is a promising technique to treat industrial wastewater discharges for selenocyanate and also remove the resulting intermediates.
作为一种营养物质，硒的安全限量与毒性限量之间的范围很窄。因此，含硒源的废水排放需要进行适当处理，同时要考虑健康问题以及严格的与硒相关的水处理标准。这项工作研究了基于层状双氢氧化物与二氧化钛耦合的光催化兼吸附系统（LDH-TiO₂）用于去除水相硒氰酸盐（SeCN⁻）的情况，硒氰酸盐难以处理且需要特定的处理程序。使用X射线衍射（XRD）、场发射扫描电子显微镜（FESEM）和热重分析（TGA）方法对合成的LDH和LDH-TiO₂复合样品进行了表征。未煅烧的LDH的XRD结果表明其为具有菱面体结构的水滑石物质，而煅烧温度升高表明其转变为无定形状态。LDH-TiO₂基质的FESEM结果表明存在圆形二氧化钛颗粒和LDH六边形层。未煅烧的LDH的TGA结果显示，在250℃之前重量逐渐下降，随后有一个短暂的平稳期，然后从320℃开始LDH重量急剧下降，净重量损失约为47%。基于表征结果和初始硒氰酸盐吸附结果，将250℃煅烧的LDH-TiO₂基质用于硒氰酸盐的光催化。当LDH:TiO₂的重量比为1.5:1且剂量为2 g/L时，观察到硒的去除率约为100%，而当LDH:TiO₂的重量比为0.5:1时，硒的去除率高达80%。硒处理效率的差异归因于在更高的LDH:TiO₂重量比中基于LDH的吸附位点增加。此外，在SeCN⁻光催化降解（PCD）过程中产生的亚硒酸盐和硒酸盐也通过吸附几乎完全被去除。使用响应面方法（RSM）对总硒去除进行的优化实验显示R²值大于0.95，预测准确率超过90%。总之，目前的研究结果表明，使用基于LDH-TiO₂的光催化兼吸附系统是一种有前景的技术，可用于处理含硒氰酸盐的工业废水排放，并去除产生的中间产物。
