Removal of crystal violet dye using a three-dimensional network of date pits powder/sodium alginate hydrogel beads: Experimental optimization and DFT calculation.

Biodegradable and very low-cost adsorbent beads were prepared from date pits powder (DP) and sodium alginate (SA). DP to SA ratios was varied (1/2, 1/4 and 1/6) and used to eliminate Crystal violet (CV) a cationic dye. Adsorbents were characterized by FTIR, SEM-EDS, UV-vis DR, TGA and the point of zero charge (pHPZC). The optimal composite beads SA@6DP show high adsorption capacities of 83.565 mg/g toward CV than SA@2DP and SA@4DP. The kinetics investigation showed that the adsorption is well described by the pseudo-second-order kinetic (R2 = 0.998). The thermodynamics and isotherms studies exhibit that the adsorption phenomenon for SA@6DP adsorbent is endothermic and significantly fitted with the Redlich-Peterson model. The experimental adsorption tests were optimized by the Box-Behnken design (BBD) which led to conclude the maximal CV removal efficiency achieved by SA@6DP was 99.873 % using [CV] = 50 mg/L, adsorbent mass = 20 mg and 48 h of contact time. The theoretical calculation proved that the CV molecules favor the mode of attack due to their electrophilic character and can accept the SA@6DP adsorbent electrons more easily to form an anti-bonding orbital. SA@6DP hydrogel beads are therefore an exceptional bio-adsorbent that offers excellent adsorption performance.

Elimination of toxic azo dye using a calcium alginate beads impregnated with NiO/activated carbon: Preparation, characterization and RSM optimization.

Nickel oxide nanoparticles supported activated carbon (AC-NiO) was fabricated using thermal activation. Then, AC-NiO composite was immobilized on alginate beads to obtain 3-dimensional network structure ALG@AC-NiO nanocomposite beads for catalytic reduction of Congo red (CR) dye. The resulting nanocomposite beads were identified by various physical techniques. The crystalline nature and dispersion of NiO nanoparticles was defined by the XRD and EDS techniques, respectively. ALG@AC-NiO beads have a Ni element content of 4.65 wt% with an average NiO particle diameter of 23 nm. The statistical approach mathematically describes the catalytic reduction of the CR dye as a function of the NaBH4 concentration, the catalyst dose and the concentration of the CR dye modeled by a BBD-RSM. According to the statistical modeling and the optimization process, the catalytic optimum conditions were obtained for NaBH4 concentration of 0.05 M, catalyst dose of 11 mg and CR dye concentration of 80 ppm who permit meet 99.67 % of CR dye conversion. The adjusted coefficient of determination (R2 = 0.9957) indicates that the considered model was quite suitable with a good correlation between the experiment and predicted.

Adsorption behavior of cationic and anionic dyes on magadiite-chitosan composite beads.

In this paper, the composite beads were obtained by the encapsulation of a lamellar polysilicate magadiite in chitosan. The composite beads were tested as adsorbents for the removal of anionic Congo red (CR) and cationic methylene blue (MB) dyes. The obtained material was characterized by different methods such as XRD, SEM, TGA and zeta potential analysis. The adsorption mechanism of both dyes was supported by UV-vis and (FTIR) spectroscopy. The results reveal that the magadiite was immobilized in the chitosan matrix by hydrogen bond and electrostatic interactions. The influence of contact time, adsorbent dose and initial concentration of dye were investigated. The adsorption kinetics of CR onto composite beads followed the linear form of pseudo-second-order model and their equilibrium data were fitted well to the linear Langmuir model as confirmed by the calculated values of R2, RMSE and SD. The adsorbed quantity registered for CR and MB dyes are 135.77 and 45.25 mg/g, respectively.

Alginate-whey an effective and green adsorbent for crystal violet removal: Kinetic, thermodynamic and mechanism studies.

In this study, a novel biocomposite beads is developed by gelling sodium alginate (ALG) solutions in acid whey (Aw). The formation of alginate-whey biocomposite (ALG-Aw) was confirmed by FTIR analysis where the corresponding spectrum showed the presence of characteristic absorption bands of both ALG and Aw. SEM analysis showed the presence of lactic bacteria immobilized in the alginate matrix leading to the formation of new porous structure. The adsorption properties of adsorbents were evaluated in crystal violet dye (CV) removal from aqueous solutions using a batch adsorption technique. The results showed that the maximum adsorption occurred at pH 6 and for an adsorbent dose of 0.4 g/L. The kinetic of CV removal onto ALG-Aw adsorbent can be described well by the pseudo-second order equation. The equilibrium adsorption data of ALG-Aw followed well the Redlich-Peterson isotherm which is coherent with the calculated R2, χ2 and ARE values. Calculated thermodynamic parameters such as Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) shown that adsorption reaction is spontaneous and it is favored at low temperatures. Interactions of CV dye molecules with ALG-Aw composite beads were examined by FTIR and UV-visible DR spectroscopy.

CuNPs-magadiite/chitosan nanocomposite beads as advanced antibacterial agent: Synthetic path and characterization.

In this work, an inorganic-organic nanocomposite was prepared by combining copper exchanged-magadiite (Cu-magadiite) with chitosan. The synthesis was carried out by direct dispersion of the Cu-magadiite in the chitosan matrix. The mixture obtained is shaped into beads with an average diameter of about 1-1.2 mm. These beads were then contacted with a solution of NaBH4 in order to reduce loaded copper ions into copper nanoparticles species. The resulting nanocomposite (Cu-NPs-magadiite/chitosan) was characterized by XRD, FTIR, SEM, TG, UV-visible DR and EDX analysis. The results show that the magadiite was completely exfoliated confirming the formation of the organic-inorganic composite. Indeed, the encapsulation of magadiite was confirmed by the SEM images, which is presented as micron free aggregates included in the cavities of a continuous polysaccharide matrix. Otherwise, they confirm also the formation of CuNPs which are probably immobilized inside the magadiite-chitosan solid matrix. The antibacterial activity against E. coli and S. aureus was highlighted by the disc inhibition method and the minimum inhibitory concentration (MIC) was determined. The CuNPs-magadiite/chitosan nanocomposite showed a very efficient bactericidal effect against both pathogen bacteria. Additionally, the MIC values obtained for nanocomposite are of 0.25 µg/L against S. aureus and of 0.50 µg/L against E. coli.

Sorption of Cu(II) Ions on Chitosan-Zeolite X Composites: Impact of Gelling and Drying Conditions.

Chitosan-zeolite Na-X composite beads with open porosity and different zeolite contents were prepared by an encapsulation method. Preparation conditions had to be optimised in order to stabilize the zeolite network during the polysaccharide gelling process. Composites and pure reference components were characterized using X-ray diffraction (XRD); scanning electron microscopy (SEM); N2 adsorption-desorption; and thermogravimetric analysis (TG). Cu(II) sorption was investigated at pH 6. The choice of drying method used for the storage of the adsorbent severely affects the textural properties of the composite and the copper sorption effectiveness. The copper sorption capacity of chitosan hydrogel is about 190 mg·g(-1). More than 70% of this capacity is retained when the polysaccharide is stored as an aerogel after supercrititcal CO2 drying, but nearly 90% of the capacity is lost after evaporative drying to a xerogel. Textural data and Cu(II) sorption data indicate that the properties of the zeolite-polysaccharide composites are not just the sum of the properties of the individual components. Whereas a chitosan coating impairs the accessibility of the microporosity of the zeolite; the presence of the zeolite improves the stability of the dispersion of chitosan upon supercritical drying and increases the affinity of the composites for Cu(II) cations. Chitosan-zeolite aerogels present Cu(II) sorption properties.