Dye recovery with photoresponsive citric acid-modified BiOCOOH smart material: Simple synthesis, adsorption-desorption properties, and mechanisms

Dye recovery is of great significance for a circular economy and sustainable development. However, green recovery strategies without secondary pollution remain a significant challenge. To resolve this issue, a light-responsive smart material (citric acid-modified BiOCOOH (m-BOCH)) was synthesized and applied for dye recovery through adsorption in the dark, and desorption under visible light. With the modification of citric acid, the adsorption level of methylene blue (MB) on m-BOCH (43.4%) was more than six times that of pure BiOCOOH (7.1%). The desorption rate was ∼90% in 120 min under 420 nm light irradiation (there was no desorption for pure BOCH). Further, the adsorption rate was improved to 83.9% and the desorption rate remained stable at an optimal pH of 10.09. Characterization results indicated that carboxyl groups were modified onto the surface of BiOCOOH and served as adsorption sites for MB. Under visible light exposure, the connections between the carboxyl groups and BiOCOOH were damaged, which led to the desorption of MB from the surface of the m-BOCH. The recovered MB exhibited a good staining effect on hepatic stellate cells (HSC) as a fresh dye. The regeneration of m-BOCH was achieved through a moderate hydrothermal process, and the adsorption and desorption capacities were restored to 80.8% and 85.7%, respectively. This research provides a novel environmentally compatible strategy for dye recovery without secondary pollution. This is a very promising treatment technique for dye effluents, which highlights the application of smart materials resource recycling for environmental remediation.

Valorization of spent brewery yeast biosorbent with sonication-assisted adsorption for dye removal in wastewater treatment

The effluent of textile industries containing synthetic dyes contributed to substantial pollution to water bodies. The biosorption process of Congo Red dye was successfully performed by integrating ultrasonication in the adsorption step with spent brewery yeast as a novel and renewable biosorbent. The adsorption process was hindered when ultrasonication was employed together with the biosorbent, indicating that desorption process had occurred. The adsorption process showed that 4 g/L of biosorbent was the optimum dosage for adsorption of 50 mg/L of Congo Red dye, and that the adsorption equilibrium fitted to the Langmuir model, with kinetics best fitted with pseudo-second order model. The maximum capacity of the adsorption was 52.6 mg/g, showing the potential of spent brewery yeast to aid in removing wastewater pollutants. Maximal Congo Red dye recovery (100%) was achieved in the sonication-assisted desorption studies using 0.01M NaOH as the eluting agent. The ultrasonication effects contributed to the efficient recovery of dye and good conversion of spent brewery yeast to biosorbent can be beneficial for treating pollution from textile wastewater.

Xanthium strumarium L. seed hull as a zero cost alternative for Rhodamine B dye removal

Treatment of polluted water has been considered as one of the most important aspects in environmental sciences. Present study explores the decolorization potential of a low cost natural adsorbent Xanthium strumarium L. seed hull for the adsorption of a toxic xanthene dye, Rhodamine B (RHB). The characterization of the adsorbent revealed the presence of high amount of carbon, when exposed to Electron Dispersive Spectroscopy (EDS). Further appreciable decolorization took place which was confirmed by Fourier Transform Infrared Spectroscopy (FTIR) analysis noticing shift in peaks. Isothermal studies indicated multilayer adsorption following Freundlich isotherm. The rate of adsorption was supported by second order kinetics directing a chemical phenomenon during the process with dominance of film diffusion as the rate governing step. Moreover paper aims at correlating the chemical arena to the mathematical aspect providing an in-depth information of the studied treatment process. For proper assessment and validation of the observed data, experimental data has been statistically treated by applying different error functions namely, Chi-square test (χ²), Sum of absolute errors (EABS) and Normalized standard deviation (NSD). Further practical applicability of the low cost adsorbent was evaluated by continuous column mode studies with 72.2% of dye recovery. Xanthium strumarium L. proved to be environment friendly low cost natural adsorbent for decolorizing RHB from aquatic system.