Phosphorylated chitin from shrimp shell waste: A robust solution for cadmium remediation.

In this work, chitin (CT) was isolated from shrimp shell waste (SSW) and was then phosphorylated using diammonium hydrogen phosphate (DAP) as a phosphorylating agent in the presence of urea. The prepared samples were characterized using Scanning Electron Microscopy (SEM) and EDX-element mapping, Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA/DTG), conductometric titration, Degree of Substitution (DS) and contact angle measurements. The results of characterization techniques reveal the successful extraction and phosphorylation of chitin. The charge content of the phosphorylated chitin (P-CT) was 1.510 mmol·kg-1, the degree of substitution of phosphorus groups grafted on the CT surface achieved the value of 0.33. The adsorption mechanisms appeared to involve electrostatic attachment, specific adsorption (CdO or hydroxyl binding), and ion exchange. Regarding the adsorption of Cd2+, the effect of the adsorbent mass, initial concentration of Cd2+, contact time, pH, and temperature were studied in batch experiments, and optimum values for each parameter were identified. The experimental results revealed that P-CT enhanced the Cd2+ removal capacity by 17.5 %. The kinetic analyses favored the pseudo-second-order model over the pseudo-first-order model for describing the adsorption process accurately. Langmuir model aptly represented the adsorption isotherms, suggesting unimolecular layer adsorption with a maximum capacity of 62.71 mg·g-1 under optimal conditions of 30 °C, 120 min, pH 8, and a P-CT dose of 3 g·L-1. Regeneration experiments evidenced that P-CT can be used for 6 cycles without significant removal capacity loss. Consequently, P-CT presents an efficient and cost-effective potential biosorbent for Cd2+ removal in wastewater treatment applications.

Effects of direct sulfonation on the catalytic activity and recyclability of novel lignin-based solid acid catalysts from agri-food waste.

Catalytic systems derived from lignin are emerging as quite efficient and profitable materials in many catalyzed transformations. However, these catalysts have been predominantly synthesized by carbonization. Alternatively, we prepared direct sulfonation lignin (DSL) and compared it to the carbonized-sulfonated lignin (CSL) catalyst, aiming to reveal the effects of direct functionalization of lignin on its catalytic performance and to simplify its preparation. Both catalysts were well characterized by several physicochemical techniques, and their catalytic activities were assessed by catalyzed esterification. Using CSL, the yield reached 94.11 % under the optimal conditions (60 °C, 4 h and 50 mg loading), while DSL yielded 93.97 % with only 2 h under the same conditions, which is attributed to the abundant catalytic active sites in DSL (0.62 mmol/g of SO3H against 0.39 mmol/g for CSL). Furthermore, the activation energies were found to be 21 and 16 kJ mol-1 for CSL and DSL, respectively, suggesting that esterification can occur with less energy input using DSL. Reusability showed that leaching of SO3H groups and mass loss are inherently responsible for deactivation. However, both lignin-based catalysts show good stability and can be reused for 4 successive cycles. Direct lignin functionalization can be an alternative to conventional catalyst processing.

Powerful cellulose phosphorylation by fertilizer-grade phosphate enables excellent methylene blue paper sorbent.

Cellulose is an interesting biopolymer offering numerous functionalization possibilities for various applications. Yet, cellulose functionalization usually involves expensive chemicals and complex processes. Here, we aim to utilize inexpensive fertilizer-grade phosphate for cellulose functionalization. Cellulose microfibers (CMF) were isolated from Giant Reed (GR) and were then phosphorylated using either a reagent-grade or a fertilizer-grade diammonium hydrogen phosphate (DAP) in the presence of urea following a water-based protocol. The effect of DAP on the phosphorylation reaction was mainly studied by conductometric titration, ICP-OES and FTIR, while further characterization was performed by SEM/EDX, TGA and XRD to investigate the morphology, composition, charge content, structure, and thermal degradation of the phosphorylated materials. It was found that cellulose phosphorylation using DAP fertilizer gave materials with the same charge content as that registered when using the reagent-grade DAP. Optimizing the reaction conditions with respect to the amount of fertilizer-grade DAP used for the phosphorylation gave high charge content (7000 mmol·g-1). The corresponding phosphorylated CMF (P-CMF) were processed into a paper and used as sorbent for methylene blue (MB) removal from aqueous solutions with different concentrations. The findings indicated that the pseudo-second-order model could be useful to assess the adsorption kinetics while the Langmuir isotherm model can suitably describe the adsorption isotherms. With fast adsorption kinetics (2-6 h), high adsorption efficiency (92-99 %) and a MB adsorption capacity of ~1200 mg·g-1 surpassing what has been reported so far for cellulose-based sorbents, the P-CMF paper holds great promises for the effective remediation of dye-contaminated wastewater effluents. Adsorption/desorption tests confirmed the reusability and regeneration of the paper with a recovery of 100 % for MB in the second cycle.