A review on chitosan/metal oxide nanocomposites for applications in environmental remediation.

A cleaner and safer environment is one of the most important requirements in the future. It has become increasingly urgent and important to fabricate novel environmentally-friendly materials to remove various hazardous pollutants. Compared with traditional materials, chitosan is a more environmentally friendly material due to its abundance, biocompatibility, biodegradability, film-forming ability and hydrophilicity. As an abundant of -NH2 and -OH groups on chitosan molecular chain could chelate with all kinds of metal ions efficiently, chitosan-based materials hold great potential as a versatile supporting matrix for metal oxide nanomaterials (MONMs) (TiO2, ZnO, SnO2, Fe3O4, etc.). Recently, many chitosan/metal oxide nanomaterials (CS/MONMs) have been reported as adsorbents, photocatalysts, heterogeneous Fenton-like agents, and sensors for potential and practical applications in environmental remediation and monitoring. This review analyzed and summarized the recent advances in CS/MONMs composites, which will provide plentiful and meaningful information on the preparation and application of CS/MONMs composites for wastewater treatment and help researchers to better understand the potential of CS/MONMs composites for environmental remediation and monitoring. In addition, the challenges of CS/MONM have been proposed.

Adsorptive removal of anionic azo dye by Al3+-modified magnetic biochar obtained from low pyrolysis temperatures of chitosan.

Magnetic γ-Fe2O3/Al3+@chitosan-derived biochar (m-Fe2O3/Al3+@CB) was prepared by introducing magnetic maghemite (γ-Fe2O3) nanoparticles and aluminum sulfate [Al2(SO4)3] into chitosan-derived biochar (CB) obtained at low pyrolysis temperatures. m-Fe2O3/Al3+@CB was used to remove typical anionic azo dye (Congo red, CR). Effects of initial CR concentration, contact time, initial pH value, background electrolytes, and temperature on CR adsorption by m-Fe2O3/Al3+@CB were studied. Compared with magnetic chitosan-derived biochar (m-Fe2O3@CB), m-Fe2O3/Al3+@CB exhibited excellent performance for a wider range of pH values (pH 1-7) and in the presence of background electrolyte. The introduction of Al3+ is an effective method for improving the properties of magnetic chitosan-derived biochar. High CR adsorption capacity (636.94 mg g-1) of m-Fe2O3/Al3+@CB could result from collaborative effect of flocculation/coagulation and electrostatic attraction. These results demonstrated that m-Fe2O3/Al3+@CB is a potential adsorbent for effective removal of organic dyes from aqueous solution due to its high adsorption capacity and convenient magnetic recovery and stronger anti-interference ability against coexisting anions in wastewater.

Magnetic Fe3O4 embedded chitosan-crosslinked-polyacrylamide composites with enhanced removal of food dye: Characterization, adsorption and mechanism.

The water solubility in acid solution, relative low adsorption capacities and unsatisfactory separation performance limit application of traditional chitosan-based adsorbents in wastewater treatment. To break the limitation, a hydrophilic magnetic Fe3O4 embedded chitosan-crosslinked-polyacrylamide composites (abbreviated as m-CS-c-PAM) were prepared by a two-step method. The m-CS-c-PAM composites were systematically characterized using SEM, XRD, FTIR, VSM, TGA and BET. Sunset yellow (SY) was selected as model food dye to investigate adsorption kinetics and thermodynamic parameters of food dye adsorption onto m-CS-c-PAM. Compared with magnetic Fe3O4/chitosan, m-CS-c-PAM can adapt to a wider range of pH (2-10) and resist the presence of inorganic salts. m-CS-c-PAM was proved to have high adsorption capacity (359.71 mg g-1) for SY dye at 298 K, much higher than magnetic Fe3O4/chitosan and many reported adsorbents. Moreover, m-CS-c-PAM could be rapidly and efficiently separated from treated solution within 15 s by an external magnet and regenerated by NaOH solution. With its excellent adsorption capacity, pH-independent adsorption capability for food dye, easy and convenient separation ability, satisfactory reusability, m-CS-c-PAM can be a promising material for food wastewater treatment.

Colloidal CdS sensitized nano-ZnO/chitosan hydrogel with fast and efficient photocatalytic removal of congo red under solar light irradiation.

Colloidal CdS sensitized nano-ZnO/chitosan (CdS@n-ZnO/CS) hydrogel was prepared and characterized extensively by XRD, SEM-EDS, TEM, UV-Vis DRS, FT-IR and TGA. The photocatalytic activity of CdS@n-ZnO/CS was evaluated with the photodegradation of congo red (CR) as an organic pollutant under solar light irradiation. The influences of initial dye concentration, catalyst dosage, recycling runs, and radical scavenger on decolorization of CR by CdS@n-ZnO/CS were investigated. 95% of CR was removed in just 1 min for 5.0 mg L-1 and 94.34% of CR was removed in 30 min for 100 mg L-1. CdS@n-ZnO/CS exhibited an excellent and ultra-fast performance toward CR removal under solar light due to the synergistic effect of adsorption by chitosan and photocatalysis by ZnO and CdS in CdS@n-ZnO/CS hydrogel. Radical trapping control experiments indicated that h+ and O2- played the major role for CR decolorization. The high performance of CdS@n-ZnO/CS hydrogel was also demonstrated under natural solar light irradiation, suggesting that CdS@n-ZnO/CS hydrogel could be used in practical wastewater treatment.

Magnetic NiFe2O4/MWCNTs functionalized cellulose bioadsorbent with enhanced adsorption property and rapid separation.

Magnetic NiFe2O4 nanoparticles and multi-walled carbon nanotubes functionalized cellulose composite (m-NiFe2O4/MWCNTs@cellulose) as a magnetic bioadsorbent was prepared and used for effectively removing Congo Red (CR) from aqueous solution. The chemical and physical properties of the prepared m-NiFe2O4/MWCNTs@cellulose were characterized by XRD, TGA, FT-IR, VSM, SEM and TEM. Batch experiments were carried out to investigate the adsorption capacity and mechanisms. Effects of different adsorption parameters such as initial CR concentration, adsorbent dosage and temperature were studied. Results demonstrated that m-NiFe2O4/MWCNTs@cellulose had high adsorption capacity for CR from aqueous solution. The obtained experimental data fitted well with the pseudo-second-order equation and followed the Langmuir isotherm model with a maximum adsorption capacity of 95.70 mg g-1 for CR. The m-NiFe2O4/MWCNTs@cellulose with rapid magnetic separation and high adsorption capacity can be a promising and recyclable engineering biomaterials for purification and treatment of practical wastewater.

High-efficiency l-lactic acid production by Rhizopus oryzae using a novel modified one-step fermentation strategy.

In this study, lactic acid fermentation by Rhizopus oryzae was investigated using the two different fermentation strategies of one-step fermentation (OSF) and conventional fermentation (CF). Compared to CF, OSF reduced the demurrage of the production process and increased the production of lactic acid. However, the qp was significantly lower than during CF. Based on analysis of µ, qs and qp, a novel modified OSF strategy was proposed. This strategy aimed to achieve a high final concentration of lactic acid, and a high qp by R. oryzae. In this strategy, the maximum lactic acid concentration and productivity of the lactic acid production stage reached 158g/l and 5.45g/(lh), which were 177% and 366% higher, respectively, than the best results from CF. Importantly, the qp and yield did not decrease. This strategy is a convenient and economical method for l-lactic acid fermentation by R. oryzae.

Effects of pellet characteristics on L-lactic acid fermentation by R. oryzae: pellet morphology, diameter, density, and interior structure.

The effects of pellet morphology, diameter, density, and interior structure on L-lactic acid fermentation by Rhizopus oryzae were characterized for different inoculum sizes and concentrations of peptone and CaCO3. Inoculum size was the most important factor determining pellet formation and diameter. The diameter decreased with increasing inoculum size, and larger pellets were observed for lower inoculum sizes. Peptone concentration had the greatest effect on pellet density, which increased with increasing peptone concentration. L-lactic acid production depended heavily on pellet density but not on pellet diameter. Low-density pellets formed easily under conditions of low peptone concentration and often had a relatively hollow structure, with a thin condensed layer surrounding the pellet and an extraordinarily loose biomass or hollow center. As expected, this structure greatly decreased production. The production of L-lactic acid increased until the density reached a certain level (50-60 kg/m(3)), in which the compact part was distributed homogeneously in the thick outer layer of the pellet and loose in the central layer. Homogeneously structured, denser pellets had limited mass transfer, causing a lower overall turnover rate. However, the interior structure remained nearly constant throughout all fermentation phases for pellets with the same density. CaCO3 concentration only had a slight influence on pellet diameter and density, probably because it increases spore germination and filamentous hypha extension. This work also provides a new analysis method to quantify the interior structure of pellets, thus giving insight into pellet structure and its relationship with productivity.

A novel magnetically separable gamma-Fe2O3/crosslinked chitosan adsorbent: preparation, characterization and adsorption application for removal of hazardous azo dye.

A novel magnetically separable adsorbent, namely magnetic gamma-Fe(2)O(3)/crosslinked chitosan composites (Mgamma-Fe(2)O(3)/CSCs), was prepared by microemulsion process and characterized by XRD, FT-IR, TGA, DSC, SEM and VSM. Adsorption of methyl orange (MO), used as a model pollutant, from aqueous solution on Mgamma-Fe(2)O(3)/CSCs was investigated. Characterization results indicated that magnetic gamma-Fe(2)O(3) nanoparticles have been introduced in Mgamma-Fe(2)O(3)/CSCs and kept intrinsic magnetic properties. The saturated magnetization (sigma(s)) of Mgamma-Fe(2)O(3)/CSCs can be expediently adjusted by changing additive dosage of gamma-Fe(2)O(3). Adsorption results showed that both nanocomposite adsorbents with weight ratio of gamma-Fe(2)O(3) to chitosan of 1:10 and 2:5 exhibited higher adsorption capacities and attained adsorption equilibria in shorter time compared with crosslinked chitosan. After adsorption, Mgamma-Fe(2)O(3)/CSCs were effectively separated from reaction solution in 10s by applying an adscititious magnetic field. Adsorption kinetics of MO on 1:10 Mgamma-Fe(2)O(3)/CSCs followed the pseudo-second-order kinetic model. Effects of both initial pH and adsorbent dosage on the adsorption of MO were remarkable in experimental conditions.