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In this study, alginate reinforced reduced graphene oxide@hydroxyapatite (rGO@HAP-Alg) hybrids have been fabricated via co-precipitation technique. The developed adsorbent was effectively utilized for the removal of Reactive Blue 4 (RB4), Indigo Carmine (IC) and Acid Blue 158 (AB158) azo dyes from aqueous solution, and found to have the adsorption efficiency of 45.56, 47.16 and 48.26 mg/g, respectively. The thermodynamic parameters demonstrated the endothermic and spontaneous nature of the adsorption process. The adsorption system was pH-dependent and showed maximum dye removal at pH 6–7, which was indicative of the electrostatic interactions, surface complexation and the hydrogen bonding mechanisms involved between the adsorbate and adsorbent during the adsorption process. Furthermore, the renewability studies demonstrated the reusability and stability of rGO@HAP-Alg hybrids up to five successive cycles. This study delivers a promising strategy for removing dye molecules and extends the potential application of rGO@HAP-Alg hybrids to treat practical dye contaminated water/wastewater.

The FMN-dependent NADH-indigo reductase gene from the thermophilic bacterium Bacillus smithii was overexpressed in Escherichia coli. The expressed enzyme functioned as a highly thermostable indigo reductase that retained complete activity even after incubation at 100 °C for 10 min. Furthermore, B. smithii indigo reductase exhibited high stability over a wider pH range and longer storage periods compared with indigo reductases previously identified from other sources. The enzyme catalyzed the reduction of various azo compounds and indigo carmine. The crystal structures of the wild-type enzyme in complex with FMN/N-cyclohexyl-2-aminoethanesulfonate (CHES) and the Y151F mutant enzyme in complex with FMN were determined by the molecular replacement method and refined at resolutions of 1.97 and 1.95 A, respectively. Then, indigo carmine molecule was modeled into the active site using the molecular docking simulation and the binding mode of indigo carmine was elucidated. In addition, the structure of B. cohnii indigo reductase, which is relatively less stable than B. smithii indigo reductase, was constructed by homology modeling. The factor contributing to the considerably higher thermostability of B. smithii indigo reductase was analyzed by comparing its structure with that of B. cohnii indigo reductase, which revealed that intersubunit aromatic interactions (F105-F172′ and F172-F105′) may be responsible for the high thermostability of B. smithii indigo reductase. Notably, site-directed mutagenesis results showed that F105 plays a major role in the intersubunit aromatic interaction.

The cross-linked enzyme aggregates (CLEAs) technology has been considered as an efficient and carrier free immobilizing method. The importance of this method comes from its simplicity and low-cost procedure, along with the utilization probability of the crude enzyme extract. The functionalized magnetic cross linked peroxidase aggregate (MNPs-TA-CLEAs-peroxidase) was prepared successfully using different aggregation agents, followed by crosslinking with glutaraldehyde. Herein, peroxidase enzyme was extracted from cabbage leaves. The beneficial of immobilized peroxidase was confirmed by decolorization studies of different types of dyes. Even the small amount of MNPs-TA-starch-CLEAs-peroxidase was able to remove a higher content of methylene blue, Congo red, indigo carmine, and malachite green (93.18, 90.0, 68.0 and 55.0%), respectively, comparing to the free enzyme. The ability of MNPs-CLEAs-peroxidase to decolorize different types of dyes, may give a suggestion of its possible usage in environmental biotechnology, especially in wastewater treatment.

A bacterial laccase having potential to work in industry without mediator is of special interest. In this work, gene (1.83kb) encoding a novel laccase from Rheinheimera sp., having potential to deink waste paper without mediator, was cloned, over-expressed and the induced 69kDa protein (RhLacc) was purified and characterized. rhlacc gene was mutated by error prone PCR and mutants were sequenced. One mutant showed protein truncation resulting in the absence of domain 3 that contains T1 copper center. It is known that redox potential of T1 is the key parameter for substrate oxidation. Overexpression of this mutant gene showed induced 41.1kDa protein (∆RhLacc) that exhibited laccase activity but in the presence of added copper, compared to RhLacc which showed activity without added copper ions. Optimum temperature for both was 55°C. However, optimum pH varied with substrates. Kinetic studies showed ∆RhLacc had lower affinity for substrates except for guaiacol and reduced kcat in comparison to RhLacc. Both were able to deink old newspaper and degrade indigo carmine without mediator. The study suggests that the novel property to deink waste paper without mediator may not depend on the redox potential of T1 but other mechanisms using domains 1 and 2 may be involved.

Laccases are multi‑copper oxidases that possess the potential for industrial wastewater treatments. In this study, a putative laccase from Sulfitobacter indolifex was recombinantly produced and characterised. The enzyme was found to be stable and active at low to ambient temperature and across a range of pH conditions. The ability of the putative bacterial laccase to catalyse the decolourisation of seven common industrial dyes was also examined. Our results showed that the putative laccase could efficiently decolourise Indigo Carmine, Coomassie Brilliant Blue R-250, Congo Red, Malachite Green and Alizarin in the presence of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) as a redox mediator. Furthermore, the use of enzyme immobilisation technology to improve the operational stability and reusability of the putative laccase was also investigated. We found that immobilising the enzyme through the cross-linked enzyme aggregate method significantly improved its tolerance towards extreme pH as well as the presence of organic solvents. This work expands the arsenal of bacterial laccases available for the bioremediation of dye-containing wastewater.

The discharge of organic dyes into the aquatic environment is a serious problem owing to the persistence of possible health risks and ecological hazards of these pollutants. This paper reports a facile method for the preparation of composite material consisting of lanthanum incorporated carboxymethylcellulose-bentonite (LCB) composite and utilized for the removal of Indigo Carmine (IC), Acid Blue 158 (AB158) and Reactive Blue 4 (RB4) dyes from water by batch adsorption techniques. The optimal conditions for the dye adsorption were found to be pH = 3, initial dye concentration: 50 mg/L and adsorbent dosage of 100 mg. The adsorption efficiency of IC, AB158 and RB4 dye molecules were 80.41%, 83.54% and 86.91% respectively. The entire adsorption process was completed within 40 min. The adsorption data fits well with the pseudo-second-order kinetic model, demonstrating the physico-chemical adsorption of the dyes on LCB matrix. The Langmuir, Freundlich, and D-R isotherm models were used to describe saturation point. The fabricated adsorbent material was characterized using PXRD, FTIR, SEM-EDAX, TGA-DSC and surface area measurements. The thermodynamic studies revealed that the adsorption was spontaneous and endothermic in nature. The LCB composite showed remarkable adsorption-desorption efficiency for dye removal in water/wastewater treatment process; hence it can be considered as a competent and potential adsorbent for dye removal.

In this study, multidye biosorption of Titan yellow (TY), Fuchsine acid (FA) and Indigo carmine (IC) in ternary mixture onto magnetic Fe3O4/chitosan nanoparticles (MFe3O4/CS NPs) and arginine-modified MFe3O4/CS NPs was investigated. Simultaneous determination of TY, IC, and FA in ternary solutions was performed by principal component-wavelet neural network (PC-WNN). Characterizations of the synthesized particles were performed by scanning electron microscopy (SEM), elemental analysis (EDAX), thermo-gravimetric analysis (TGA), vibrating sample magnetometer (VSM), Fourier transform infrared (FT-IR) spectroscopy and BET surface area analysis. Result VSM indicate the saturation magnetization values of bare Fe3O4 and arginine-modified magnetic chitosan nanoparticles were about 55.00, 23.04 emu/g, respectively. Also result of BET analysis showed chitosan, MFe3O4/CSNPs, and arginine-modified are nonporous and specific surface area for arginine-modified is more than chitosan, MFe3O4/CSNPs. Response surface methodology (RSM) with Box-Behnken design was used to optimize experimental parameters (biosorbent dose, pH, and time). At optimum conditions, maximum total biosorption capacity of MFe3O4/CSNPs and arginine-modified MFe3O4/CSNPs for anionic dyes was 0.385 and 0.681 mmol g−1, respectively. Arginine-modified magnetic Fe3O4/CSNPs biosorption capacity was twice better than that of magnetic Fe3O4/CSNPs. The biosorption processes were kinetically followed by a pseudo-second order model. Fourteen isotherms were also fitted to biosorption equilibrium data.

Oxidation of phenolic compounds is an urgent need in textile industry, biological refinements, pulp and paper production. In present study, a laccase was purified from symbiotic bacterium of Bacillus sp. CF96 existing in termite digestive system. The extracellular laccase was purified via amnion sulfate precipitation, membrane dialysis, and ion exchange chromatography. The results showed that the Bacillus CF96 laccase possesses a molecular mass of 63 kDa, an optimal pH and temperature of 8.0 and 60 °C. Results showed that Zn2+, Mn2+ and Fe2+ were considered as the activator ions, while SDS was the main inhibitor. Using syringaldazine (SGZ) as substrate, the half-life of laccase at optimal temperature was 148 min; Km and Vmax were 0.737 μM and 100.5 U/mg. In addition, the enzyme showed a high effect on indigo dye with 90% bleaching capacity compared to control. In conclusion, the laccase has potential applications in industries under the provided optimal conditions.

Chitosan/cobalt-silica (Co-MCM) nanocomposites were synthesized for the purification of effluent by adding 5, 15 and 25mL of Co-MCM solution to the aqueous chitosan solution for the formation of chitosan/Co-MCM-5, chitosan/Co-MCM-15 and chitosan/Co-MCM-25, respectively. These different nanocomposites were characterized by FESEM, EDS, X-ray crystallography and IR spectrophotometer and employed for the adsorption of various dyes (methyl orange, acridine orange, indigo carmine and congo red). The respective nanocomposites showed good adsorption toward methyl orange, indigo carmine and congo red while all nanocomposites were inactive for acridine orange dye. Among the nanocomposites, chitosan/Co-MCM-15 showed the highest adsorption performance which might be due to ideal dispersion of Co-MCM inside the chitosan polymer host. Chitosan/Co-MCM-15 exhibited high adsorption for methyl orange as compared to indigo carmine. We have further checked the biological potential of chitosan/Co-MCM nanocomposites against gram positive and negative bacteria as well as multi drug resistant bacteria. The results favor the strongest bioactivities of chitosan/Co-MCM-15 against various gram positive and gram negative bacteria as well as multi drug resistant bacteria, which further suggest the ideal dispersion of Co-MCM in chitosan polymer host and is responsible for the improvement of both adsorption as well as biological performance.

Sodium carboxymethyl cellulose (NaCMC) and chitosan (CS) are successfully combined via amidation, and the obtained product, CMC-CS-A, is used for the adsorption of toxic indigo blue (IB) for the first time. The results of control experiments indicate that the adsorption performance of CMC-CS-A is superior to that of NaCMC, CS, and the composites of NaCMC and CS integrated via electrostatic attractions (CMC-CS-E), which can be attributed to the unique interconnected porous network structure of the as-prepared CMC-CS-A. The mass fraction of CS in the CMC-CS-A is also investigated to achieve the best adsorption of IB, and it reveals that satisfactory removal of IB can be achieved at the CMC-CS-A (50 wt%). Important parameters such as contact time, temperature and initial concentration are discussed in detail in this work. Finally, adsorption isotherms and adsorption kinetics are investigated and compared by using classic models, and the results indicate that the adsorption fits well with the Langmuir isotherm model and the pseudo-second-order kinetic model. It opens a new avenue for the effective and convenient treatment of textile wastewater with integrated natural biopolymers.

Chitosan/copper oxide (CS/CuO) composite spheres were prepared by simple mixing of CuO nanomaterials in CS solution followed by dropwise addition to NH4OH solution. The characterizations of all the prepared spheres were carried out by FESEM, EDS, XRD, XPS, and FTIR analyses while the thermal properties were analyzed by TGA. Further the ability of composite spheres was tested as an easily removable pollutant adsorbent from water containing different dyes and compared with pure CS. Composite spheres were found to be the best adsorbent when applied to remove indigo carmine (IC), congo red (CR) and methyl orange (MO) from water. Amongst the three dyes, CS/CuO composite spheres were more selective toward MO adsorption. CS/CuO composite spheres also displayed significant antibacterial activity by inhibiting Pseudomonas aeruginosa growth. Thus the fabricated composite spheres can be used as a biosorbent in the future.

A purified papaya laccase was immobilized in chitosan beads using entrapment approach and its physico-chemical properties were investigated and compared with that of free enzyme. Increase in properties of the laccase such as optimum temperature (by 10 °C), thermostability (by 3-folds) and optimum pH (from 8.0 to 10.0) was observed after immobilization. Immobilization led to increased tolerance of enzyme to a number of metal ions (including heavy metals) and organic solvents namely, ethanol, isopropanol, methanol, benzene and DMF. The catalytic efficiency (Kcat/Km) of the immobilized enzyme was found to increase more than ten folds, in comparison to that of the free enzyme, with hydroquinone as substrate. Immobilization of laccase also led to improvement in dye decolorization such that the synthetic dye indigo carmine (50 μg/ml) was completely decolorized within 8h of incubation as compared to that of the free laccase which decolorized the same dye to only 56% under similar conditions. Thus, immobilization of laccase into chitosan beads led to tremendous improvement in various useful attributes of this enzyme thereby making it more versatile for its industrial exploitation.

In the present study, a novel hydrogel based on the polysaccharide, ‘Karaya gum’ has been synthesised by graft copolymerization and evaluated as an adsorbent for the removal of ionic dyes from aqueous solution. The hydrogel was made by simultaneous grafting and cross linking of Karaya gum using 2-(dimethylamino)ethyl methacrylate (DMAEMA) and N,N′-methylene-bis-acrylamide via microwave irradiation. The graft copolymer gel was characterized by FTIR, TGA, SEM techniques. The swelling of the gel studied in buffer media of varying pH revealed a pH responsive behaviour with a maximum swelling in neutral pH and a minimum swelling at pH 1.2. The temperature dependent swelling study indicated 40 °C as the lowest critical solution temperature. Kinetic studies indicated the swelling to be a second order process with Fickian diffusion as the water transport mechanism. The adsorption studies indicated maximum adsorption capacity of 89.28 and 101.42 mg/g towards methylene blue and indigo carmine respectively. The dye adsorption data is found to fit well with pseudo- second order kinetic model and the Freundlich adsorption isotherm model. The adsorption was found to be a multistep process with surface adsorption followed by intraparticle diffusion. Thermodynamic studies revealed the adsorption of dyes to be spontaneous.

Laccases are copper-containing enzymes which possess a promising potential in many industrial and environmental applications. Here we describe the cloning, extracellular expression and characterization of a novel non-blue laccase from Bacillus amyloliquefaciens in Pichia pastoris. The recombinant enzyme was secreted into the culture supernatant with high activity. It lacks the absorption band at 610 nm typical for blue laccases. However, electron paramagnetic resonance (EPR) spectrum proved the existence of type 1 copper center that was not detectable in the UV-visible spectrum. Metal content analysis revealed that the enzyme contains two copper ions, one iron ion and one zinc ion per protein molecular, suggesting that it is a novel non-blue laccase. The pH and temperature optima of the recombinant laccase were 6.6 and 60°C, respectively, and it was stable at pH 9.0 for 10 days. The enzyme activity was slightly activated by NaCl with concentration up to 200 mM. The purified laccase showed high efficiency in decolorizing reactive black 5 and indigo carmine, achieving more than 93% decolorization after 1h. The extreme robustness of the recombinant B. amyloliquefaciens laccase offers several advantages over most fungal laccases in various industrial applications.

This research paper reports the photocatalytic properties of Zn–SiO 2 –Eu 3+ and sodium alginate (Alg) based nanocomposites for the degradation of indigo carmine dye. Initially, Eu 3+ doped ZnS–SiO 2 nanophorphor was synthesized and after that it was incorporated within the grafted crosslinked polymer matrix of Alg with acrylamide- co -acrylic acid in different concentrations. Synthesized materials were characterized using XRD, Raman spectroscopy, FTIR, SEM/EDX, TEM and UV–vis diffuse reflectance spectroscopy. XRD and TEM analyses confirmed the formation of nanoparticles as well as the uniform distribution of the nanoparticles within the polymer matrix. The UV–vis and UV–vis DRS spectral analysis indicated that Eu 3+ doping causes a red-shift in the absorption band, resulting in the reduction in band gaps. The synergic effect of ZnS and Eu 3+ in the SiO 2 evidenced the photocatalytic performance of the catalyst. Alg-cl-poly(AAM- co -MAA)/ZnS–SiO 2 –Eu 3+ nanocomposites were found to be very effective for the degradation of indigo carmine under visible light. Highest photocatalytic performance (93.4%) was shown by the nanocomposite with the 20% concentration of the nanoparticle after 5 h. The photocatalytic activity was mainly attributed to the intense light absorption in the visible region and narrow band gap energy.