The study analyzed the sorption effectiveness of reactive dyes, Reactive Black 5 (RB5) and Reactive Yellow 84 (RY84), onto non-cross-linked chitosan beads (CHs) and onto CHs cross-linked with glutaraldehyde (ALD) i.e., ALD-CHs and epichlorohydrin (ECH) i.e., ECH-CHs. The study enabled determination of the optimal ratio of the cross-linking agent to chitosan and the optimal pH of the sorption process (from the range of 1:10–10:1, to 2–12, respectively). The time needed to reach the equilibrium concentration reached 504 h. Satisfactory effects of RB5 and RY84 sorption were achieved after 24 h sorption. Data were described with the heterogenous Langmuir’s model (double Langmuir’s equation). For RB5 dye, the most effective sorbent turned out to be CHs – the maximum sorption capacity reached 2025.11 (mg/g). For the other sorbents, ALD-CHs and ECH-CHs, the capacity accounted for 1797.0 mg/g and 1816.1 mg/g, respectively. In the case of RY84 dye, the most effective sorbent appeared to be ECH-CHs – 2234.3 mg/g. For CHs and ALD-CHs, the highest sorption capacities against RY84 reached 1774.2 and 2000.1 mg/g, respectively.

This manuscript presents results of a study on sorption effectiveness of orthophosphate and nitrate III and V in an equimolar mixture of P–PO4, N–NO2 and N–NO3 using chitosan in the form of hydrogel beads. Analyses were carried out for: the effect of pH on sorption intensity of orthophosphate and of nitrate III and V onto chitosan, sorption kinetics onto chitosan, and the maximum sorption capacity of P–PO4, N–NO2 and N–NO3 by chitosan in a mixture.The most effective sorption of P–PO4, N–NO2 and N–NO3 was observed at pH 4. In turn, at pH 6–11 the sorption of orthophosphate and nitrate onto chitosan proved ineffective. P–PO4, N–NO2 and N–NO3 sorption kinetics was best described by the pseudo-second order model. The model of intraparticle diffusion fitting to experimental data demonstrated that the process of orthophosphate and nitrate sorption onto chitosan proceeded in 2 phases, i.e. 1 – adsorption and 2 – absorption.A phenomenon of the partial release of P–PO4, N–NO2 and N–NO3 after a specified period of time was observed in the study, which was due to a change in solution pH induced by the sorbent. The period after which desorption occurred was 120min in the case of phosphates and 60min in the case of nitrates III and V. The quantity of bound sorbate (a mixture of orthophosphate and nitrate) was the highest in the 60th minute of sorption.The study demonstrated evident competition between H2PO4−, NO2− and NO3− ions. The affinity of orthophosphate and nitrate to the sorption centers of chitosan could be ordered as follows: P–PO4>N–NO2>N–NO3. Sorption equilibrium isotherms were best described by a heterogeneous Langmuir’s model. In the equimolar mixture of P–PO4, N–NO2 and N–NO3, the sorption capacity of 1g of chitosan reached 0.507mmol H2PO4−/g, 0.373mmol NO2−/g and 0.350mmol NO3−/g, which means a total of 1.23mmol nutrients

This study aimed to investigate the sorption of anionic dyes (Reactive Black 5, Reactive Yellow 84, Acid Red 18, and Acid Yellow 23) by cotton fibers aminated with epichlorohydrin and ammonia water (ACFs) as well by unmodified cotton fibers (CFs). CFs and ACFs were characterized based on FTIR, elemental analysis (C/N content) and pH_PZC. The effect of solution pH (pH 2–11) and contact time on the removal of dye was studied as well. The kinetic experimental data were fitted to pseudo-first order, pseudo-second order, and intraparticle diffusion model. Equilibrium isotherms were analyzed based on Langmuir and Freundlich isotherms. The efficiency of dye sorption on CFs was the most effective at pH 2, whereas on ACFs—at pH 3–4. ACFs and CFs changed the pH value of the sorption solution. The system tended to obtain a pH value close to the pH_PZC value of the sorbent (pH_PZC = 7.85 for CFs/pH_PZC = 8.15 for ACFs). ACFs had a shorter dye sorption equilibrium time compared to the CFs. The sorption of dyes on cotton sorbents proceeded in 2 main phases. The best match to the experimental data was shown by the pseudo-secondary model. Having amine functional groups, the ACFs ensured far better sorption of anionic dyes than CFs did. The maximum Reactive Black 5 sorption capacity of ACFs was Q_max = 36.77 mg/g, which was 1240% higher than that of CFs (Q_max = 2.74 mg/g).