Chitosan-based microparticles for immobilization of TiO2 nanoparticles and their application for photodegradation of textile dyes

The present paper deals with removal and photocatalytic degradation of the textile dyes by TiO2 nanoparticles immobilized onto chitosan-based microparticles. The microparticles composed of chitosan (Ch) and poly(methacrylic acid) (PMA) were fabricated for the first time by inverse suspension polymerization. They were utilized for colloidal TiO2 nanoparticles immobilization, synthetized by acidic hydrolysis of TiCl4. To evaluate the potential application of Ch/PMA/TiO2 microparticles for treatment of textile wastwaters, their photocatalytic activity was examined by degradation assessment of three different groups of anionic azo dyes in aqueous solutions under solar light simulating source. FTIR analysis revealed that Ch and PMA were incorporated in the polymer network. SEM and optical microscopy confirmed their spherical shape. Under illumination, Ch/PMA/TiO2 microparticles completely removed dyes C.I. Acid Orange 7, C.I. Acid Red 18, C.I. Acid Blue 113, C.I. Reactive Black 5, C.I. Direct Blue 78, while removal degree of C.I. Reactive Yellow 17 was 75%. It was found that pH had significant influence on the photocatalytic activity of Ch/PMA/TiO2 microparticles. Increase of solution pH from acidic to alkaline, lead to decrease in photodegradation rate of C.I. Acid Orange 7 during the first hours of illumination. After three illumination cycles, removal degree of C.I. Acid Orange 7 was maintained at remarkably high level (95% at pH 5.60 and 100% at pH 2.00 and 8.00), indicating that microparticles could be reused without significant loss of photocatalytic efficiency. (C) 2016 Elsevier Ltd. All rights reserved.</p

Immobilization of lipase from Candida rugosa into copolymer hydrogels of poly(N-isopropylacrylamide-co-itaconic acid) synthesized in the presence of surfactants

To overcome the problems of free enzyme application as catalysts in chemical reactions, i.e., high costs of isolation and purification processes, high sensitivity to process conditions, insufficient enzyme stability etc., different immobilization techniques need to be used. Immobilization to/within solid support improves enzyme stability decreasing its denaturation. This paper deals with hydrogels of N-isopropylacrylamide and itaconic acid with incorporated nonionic surfactants (Triton X-100, Brij 30 and Tween 80) synthesized in distilled water at room temperature by free radical polymerization. These hydrogels were used as supports for immobilization of enzyme, lipase from Candida rugosa by post-entrapment method. The aim was to investigate the effect of the non-ionic surfactants on the lipase binding capacity, as well as on its hydrolytic activity. In order to characterize the obtained hydrogels, FT-IR analysis has been performed. Further, the swelling behaviour of these samples in buffer solution of pH 6.80 has been investigated. The dynamic-mechanical properties of hydrogels have been studied, too. The immobilized lipase showed somewhat reduced hydrolytic activity, compared to the activity of free lipase as well as in comparison to the lipase immobilized to the reference sample (sample synthesized under the same polymerization conditions, but in the absence of surfactants). It was concluded that the addition of surfactants increased the hydrogel mesh size. The surfactant addition did not affect the dynamic-mechanical properties of the investigated hydrogels. The largest percentage of specific activity and yield of activity were presented by the reference sample, too. It is obvious that the absence of surfactants charged groups has no influence on the lipase binding capacity, and the obtained activity yields are to be expected.U radu je ispitana imobilizacija lipaze iz Candida rugosa u hidrogel poli(N-izopropilakrilamid-ko-itakonska kiselina) sintetisane u prisustvu nejonskih površinski aktivnih materija. Pri sintezi je varirana vrsta i sadržaj površinski aktivnih materija. Ispitana su mehanička svojstva sintetisanih hidrogelova i urađena je FT-IR analiza. Imobilizacija lipaze je izvedena bubrenjem prethodno sintetisanih hidrogelova u rastvoru lipaze, a zatim je ispitan uticaj dodatka površinski aktivnih materija pri sintezi nosača na kapacitet uklapanja lipaze u hidrogel i na aktivnost tako uklopljene lipaze. Imobilisana lipaza iz Candida rugosa je pokazala umanjenu hidrolitičku aktivnost, kako u odnosu na aktivnost slobodne lipaze, što je i očekivano, tako i u odnosu na aktivnost lipaze imobilisane u referentni hidrogel, sintetisan bez prisustva površinski aktivnih materija

Photocatalytic Degradation of C. I. Acid Orange 7 by TiO2 Nanoparticles Immobilized onto/ into Chitosan- Based Hydrogel

Photocatalytic degradation of dye C.I. Acid Orange 7 in aqueous solution using TiO2/hydrogel nanocomposite under solar light simulating source was studied. Hydrogel based on chitosan, itaconic and methacrylic acid was modified with colloidal TiO2 nanoparticles synthetized by acidic hydrolysis of TiCl4 and commercial Degussa P25 TiO2 nanoparticles. SEM/EDX analysis confirmed the presence of TiO2 nanoparticles onto/into hydrogel. It was found that both types of photocatalysts efficiently removed the dye from solution, but sorption rates and photodegradation efficiency were higher in the case of colloidal TiO2 nanoparticles. They ensured complete discoloration of dye solution. The efficiency of the reused TiO2/hydrogel nanocomposite showed that photodegradation activity was maintained at satisfactory level after three repeated cycles of illumination. POLYM. COMPOS., 35:806-815, 2014. (c) 2013 Society of Plastics Engineer

Sorption of zinc by novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid

Novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were applied as adsorbents for the removal of Zn(2+) ions from aqueous solution. In batch tests, the influence of solution pH, contact time, initial metal ion concentration and temperature was examined. The sorption was found pH dependent, pH 5.5 being the optimum value. The adsorption process was well described by the pseudosecond order kinetic. The hydrogels were characterized by spectral (Fourier transform infrared-FTIR) and structural (SEM/EDX and atomic force microscopy-AFM) analyses. The surface topography changes were observed by atomic force microscopy, while the changes in surface composition were detected using phase imaging AFM. The negative values of free energy and enthalpy indicated that the adsorption is spontaneous and exothermic one. The best fitting isotherms were Langmuir and Redlich-Peterson and it was found that both linear and nonlinear methods were appropriate for obtaining the isotherm parameters. However, the increase of temperature leads to higher adsorption capacity, since swelling degree increased with temperature

Hydrogel based on chitosan, itaconic acid and methacrylic acid as adsorbent of Cd2+ ions from aqueous solution

A hydrogel has been synthesized by ionic crosslinking of chitosan (Ch) with itaconic acid (IA), followed by a free radical polymerization and crosslinking of Ch/IA network by adding methacrylic acid and the crosslinker. The resulting material (Ch/IA/MAA hydrogel) was characterized by spectral (Fourier transform infrared (FTIR)), thermal (thermogravimetric analysis (TGA)) and structural (SEM/EDX and atomic force microscopy (AFM)) analyses. The prepared hydrogel was investigated as potential adsorbent for removal of Cd2+ ions from aqueous solution. The effect of various physico-chemical parameters such as pH, adsorbent dosage, adsorbate concentration and contact time was studied in batch experiments. The results of spectral analyses of Cd-loaded hydrogel have shown that active functional groups are -NH2, -OH and -COOH. SEM/EDX analysis and AFM surface topography and phase images indicated that apart from the adsorption on the surface of the hydrogel, sorption takes place in the bulk, as well. The experimental kinetic and equilibrium data were better fitted by pseudo-second order kinetic model and Langmuir adsorption isotherm. The parameters obtained in thermodynamic studies showed that the adsorption of Cd2+ on Ch/IA/MAA hydrogel was spontaneous and exothermic in nature. Desorption studies were carried out using acid leaching (HNO3) and it has been shown that the regenerated hydrogel can be reused three times without any loss of adsorption capacity. The maximum adsorption of 285.7 mg/g has been obtained at pH 5.5 and the results of adsorption/desorption experiments implies that the Ch/IA/MAA hydrogel may be used as efficient sorbent for removal of Cd2+ ions from aqueous solution

Removal of Cu2+ ions using hydrogels of chitosan, itaconic and methacrylic acid: FTIR, SEM/EDX, AFM, kinetic and equilibrium study

A removal of Cu2+ ions from aqueous solutions onto hydrogels of chitosan. itaconic and methacrylic acid has been investigated using batch adsorption technique. The extent of adsorption was investigated as a function of pH, adsorbent dose, initial metal ion concentration, contact time and temperature. The FIR spectra showed that -NH2, -OH and -COOH groups are involved in the Cu2+ ions adsorption. The surface topography changes were observed by AFM, where the phase images indicated that sorption takes place on the surface of the hydrogel and in the bulk. Pseudo-first order, pseudo-second order and intraparticle diffusion models were analyzed and showed that the Cu2+ ions adsorption followed pseudo-second order kinetics. The equilibrium data were analyzed using Langmuir, Freundlich and Redlich-Peterson isotherms and the best interpretation was given by Redlich-Peterson. The adsorption capacity was found to be 122.59 mg/g, based on the non-linear Langmuir isotherm. Based on the separation factor. R-L, the Cu2+ ion adsorption is favorable, while the low activation energies indicate physisorption. Desorption experiments, done with a nitric acid, showed that the investigated hydrogels could be reused without significant losses of the initial properties even after three adsorption-sorption cycles

Economics of Digital Transformation

The papers published in this monograph present best papers presented at the first conference of the Faculty of Economics and Bussiness of University of Rijeka organized on the topic of “Economics of digital transformation” from 2nd to 4th of May, 2018 in Opatija, Croatia (www.edt- conference.com). During the three days of the conference more than 50 researchers from European region contributed with their presentations. We are particularly proud on the results of our doctoral workshop where nine young researchers presented their research while five papers were published in the monograph. In this way we are building our future research capacities and expose young researchers to rigorous scientific challenge

Economics of Digital Transformation

The papers published in this monograph present best papers presented at the first conference of the Faculty of Economics and Bussiness of University of Rijeka organized on the topic of “Economics of digital transformation” from 2nd to 4th of May, 2018 in Opatija, Croatia (www.edt- conference.com). During the three days of the conference more than 50 researchers from European region contributed with their presentations. We are particularly proud on the results of our doctoral workshop where nine young researchers presented their research while five papers were published in the monograph. In this way we are building our future research capacities and expose young researchers to rigorous scientific challenge