Contamination of water by heavy metals is a major environmental concern due to the potential ecological impact on human health and aquatic ecosystems. In this work, we studied the chemical modification of various fruit peels such as banana (BP), granadilla (GP), and orange ones (OP) in order to obtain novel bio-adsorbents to improve the removal of Zn(II) ions from 50 mg·L⁻¹ synthetic aqueous solutions. For this purpose, sodium hydroxide and calcium acetate were employed to modify the fruit peels. The moisture, extractives, lignin, hemicellulose, and cellulose contents of the raw materials were determined according to ASTM standards. The obtained bio-adsorbents were characterized by scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results showed the OP bio-adsorbents performed better, especially when the concentration of the modifier solutions increased, e.g., the OP particles modified using 0.8 M NaOH and Ca(CH₃COO)₂ solutions resulted in 97% removal of Zn(II) contaminating ions and reached a maximum adsorption capacity of 27.5 mg Zn per gram of bio-adsorbent. The adsorption processes were found to follow a pseudo-second order model. The error function sum of square error indicated the Freundlich isotherm (non-linear regression) as best fit model. The obtained results are particularly interesting for material selection in wastewater treatment technologies based on contaminant adsorption.

Edible films based on biopolymers are used to protect food from adverse environmental factors. However, their ample use may be hindered by some challenges to their mechanical and antimicrobial properties. Despite this, in most cases, increasing their mechanical properties and antibacterial activity remains a relevant challenge. To solve this problem, a possible option is to fill the biopolymer matrix of films with a functional filler that combines high reinforcing and antibacterial properties. In this work, biocomposite films based on a mixture of chitosan and cassava starch were filled with a hybrid filler in the form of bentonite clay particles loaded with ginger essential oil (GEO) in their structure with varied concentrations. For this purpose, GEO components were intercalated into bentonite clay interlayer space using a mechanical capture approach without using surface-active and toxic agents. The structure and loading efficiency of the essential oil in the obtained hybrid filler were analyzed by lyophilization and laser analysis of dispersions, ATR-FTIR spectroscopy, thermogravimetry, and X-ray diffraction analysis. The filled biocomposite films were analyzed using ATR-FTIR spectroscopy, optical and scanning electron spectroscopy, energy dispersive spectroscopy, mechanical analysis under tension, and the disk diffusion method for antibacterial activity. The results demonstrated that the tensile strength, Young’s modulus, elongation at the break, and the antibacterial effect of the films increased by 40%, 19%, 44%, and 23%, respectively, compared to unfilled film when the filler concentration was 0.5–1 wt.%.

In this work, three carboxymethyl starches (CMS) were obtained by the two-step reaction process of carboxymethylation with different degrees of substitution (0.16, 0.33, and 0.36). From these samples, (bio)polyelectrolyte complexes ((bio)PECs) were obtained with chitosan (Chit) by the mixing of individual solutions of polymers (0.25 wt.%) at different volume ratios. The effect of the biopolymer and ionized groups of z ratios, pH, and degree of substitution of CMS in the formation of PEC were evaluated by turbidimetry and dynamic light scattering. The results showed that increasing the amount of CMS samples (ratio of z) led to an increase in the efficiency of the formation of (bio)PEC using CMS with a high DS value. Using the turbidimetry method for the chitosan and CMS mixtures, it was observed that the formation of (bio)PEC is divided into four transition zones delimited by pH transition points, and the stoichiometric complexation (z = 1) is achieved at a pH that displayed morphological changes “pH_morph”, which is a single point for Chit:CMS 1, and for Chit:CMS 2 and Chit:CMS 3, this is a range of 4.9–6.4 and 4.3–6.4, respectively. Analysis of the structural properties of the structures of (bio)PECs by dynamic light scattering was characterized by monomodal distribution, and the main observed effect was associated with an increase in the value of D_avg with an increase in the ratio of Chit:CMS.

Bio-based materials from rice husk were obtained by processing rice rusk with acid (HCl, H2SO4, and H3PO4 0.1 mol·L-1), alkali (NaOH 0.1 mol·L-1, 0.25 mol·L-1 and 0.5 mol·L-1) and water. The chemical composition of rice husk, obtained from its bio-based materials and generated wastewater, was studied. After obtention of bio-based materials, wastewater produced in rice husk processing was treated by heterogeneous photo-Fenton. Substances soluble in water, pentosanes, lignin, cellulose, easy and difficult hydrolyzable polysaccharides were determined. Results showed that the chemical composition of rice husk and bio-based materials processed with water are similar. It is shown that bio-based materials processed with alkali contain more lignin, pentosans, and cellulose than when it is processed with water and acid. Wastewater, obtained while processing rice husk, was treated by a heterogeneous photo-Fenton process using SiO2-based RH-Fe-300 obtained from rice husk under visible and solar irradiation in the presence of hydrogen peroxide. Wastewater treatment by photo-Fenton presents decreased color, turbidity, phenolic compounds, and COD by 30-99% compared to the initial data. Achieved results are important for obtaining bio-based materials from rice husk and the treatment of wastewater generated during their production.

Biopolymeric films based on chitosan and starch offer an ecological alternative for food protection. Nevertheless, their practical application is often limited by their low mechanical properties and high solubility in aqueous solutions, due to weak interactions between the chains of the biopolymers. One approach to resolve this problem is to obtain biopolymeric films based on (bio)polyelectrolyte complex ((bio)PEC). These films exhibit stronger electrostatic interactions and homogeneous biopolymeric structure. In this study, films based on (bio)PEC were obtained by the casting method, using chitosan and carboxymethyl cassava starch with different degrees of substitution with a biopolymer concentration of 2.5 wt.% at pH = 6. The obtained films were analyzed using the optical and scanning microscopy, color method, ATR-FTIR spectroscopy, thermogravimetry, mechanical analysis under tension, solubility in water, simulated gastric fluid (SGF), and phosphate-buffered saline (PBS) solutions, and contact angle of water. The results demonstrated that the tensile strength and Young’s modulus of films based on (bio)PEC increased by 2–4 times, and the elongation at break by 20% compared to films based on a mixture chitosan and starch. This is due to the increase in the attraction between oppositely charged polyelectrolytes in (bio)PEC films. Additionally, the solubility of (bio)PEC films was reduced by ~40%, 35% and 70% in water, SGF and PBS solutions, respectively, when the carboxymethyl starch with highest degree of substitution was used, and z was near to 1.

Rice husk is used as a biosorbent due to its chemical composition and irregular surface. In this work, we studied the chemical modification of rice husk in order to improve the removal of Cr(VI), Cu(II), and Zn(II) ions from synthetic solutions. Rice husk was treated with distilled water (RH-H2O), solutions of sodium hydroxide 0.5, 0.25, and 0.1 mol × L−1, and different acids (0.1 mol × L−1 HCl, H2SO4, H3PO4). The biosorbents from each treatment with the highest metal ion removal efficiency were selected for kinetic and thermodynamic studies. The results showed that the greatest biosorption efficiency for Cr(VI), Cu(II), and Zn(II) ions was achieved with sodium hydroxide treatment. Furthermore, Cu(II) and Zn(II) ions were more effectively removed from aqueous solutions than Cr(VI) by the studied samples. Kinetic studies indicated that the process followed a pseudo-second-order model, with rate constants of 0.61, 4.11, and 4.75 g·(mmol·s)−1 for Cr(VI), Cu(II), and Zn(II), respectively. Analysis of the kinetic data showed that the biosorption of Cr(VI), Cu(II), and Zn(II) onto biosorbents derived from rice husk was governed by a mixed-diffusion process and interaction with functional surface groups. The biosorption process for Cu(II) and Zn(II) was found to be spontaneous, whereas it was not spontaneous for Cr(VI).