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.