Hyperbranched-Polyethylenimine-Functionalized Coal Fly Ash as an Adsorbent for the Removal of Hexavalent Chromium and Reuse as a Dye Photocatalyst.

Coal fly ash (CFA) has been extensively researched as an adsorbent for heavy metals, but its application is limited by its low adsorption capacity. The modification of CFA with hyperbranched polymers results in improved adsorption capacities. Hyperbranched polyethylenimine (HPEI) is a hyperbranched polymer containing NH2 groups that can bind with heavy metal ions through complexation or electrostatic interactions. In this study, CFA-HPEI adsorbents with various HPEI loadings (1-5%) were prepared and evaluated for the removal of Cr(VI). The successful incorporation of HPEI onto CFA was confirmed using Fourier transform infrared, elemental analysis, and X-ray photoelectron spectroscopy (XPS). The 3% CFA-HPEI loaded adsorbent resulted in optimum results when the effect of pH and adsorbent dosage was studied. The pseudo-second-order kinetics model best described the adsorption kinetics at an initial concentration of 20 mg/L. The Freundlich adsorption isotherm model best fitted the equilibrium adsorption data with a maximum adsorption capacity of 85.93 mg/g. The Cr-loaded adsorbent was reused as a photocatalyst to degrade methylene blue (MB) in the presence of visible light. The loaded adsorbent degraded 98.9% of MB (5 mg/L) within 180 min and was accompanied by compounds with m/z of 173 and 234, corresponding to the intermediate degradation of Azure A. The XPS analysis confirmed the coexistence of Cr(III) and Cr(VI) on the surface of the adsorbent. In addition, the loaded adsorbent exhibited good stability following MB degradation with no structural changes observed. Thus, CFA-HPEI adsorbents can be utilized as low-cost adsorbents for the remediation of toxic Cr(VI) from water and wastewater. The Cr-loaded CFA-HPEI adsorbent can be effectively reused as a photocatalyst, thus reducing environmental pollution.

Rooibos tea waste binary oxide composite: An adsorbent for the removal of nickel ions and an efficient photocatalyst for the degradation of ciprofloxacin.

In this study, rooibos tea waste (RTW) incorporated with a binary oxide (BO; Fe2O3-SnO2) has been reported for the first time as a highly efficient adsorbent material for the elimination of Ni(II) ions. The as-synthesised rooibos tea waste-binary oxide (RWBO) composite adsorbent was characterised using miscellaneous techniques such as FTIR, XRD, SEM, EDX, TGA, BET, and XPS. The RWBO was then tested for the removal of Ni(II) in a batch adsorption experiment. The composite adsorbent showed a great removal efficiency of about 99.75% for Ni(II) ions at 45 °C, 180 min agitation time, pH 7, and dosage of 250 mg. The adsorption process was found to be endothermic and spontaneous. Also, the spent adsorbent [RWBO-Ni(II)] was found to be solar light active with a narrow band gap of 1.4 eV. It was further used as a photocatalyst for the photocatalytic abatement of 10 mg/L ciprofloxacin with an extent of degradation of 83% obtained after 150 min. In addition, the extent of mineralisation of the ciprofloxacin by the spent adsorbent as obtained from the TOC data was found to be 64%. Overall, the RWBO composite adsorbent lends itself as an efficient, eco-friendly and promising material for environmental remediation.

Synthesis and Characterization of MC/TiO2 NPs Nanocomposite for Removal of Pb2+ and Reuse of Spent Adsorbent for Blood Fingerprint Detection.

The removal of toxic heavy metals from wastewater through the use of novel adsorbents is expensive. The challenge arises after the heavy metal is removed by the adsorbent, and the fate of the adsorbent is not taken care of. This may create secondary pollution. The study aimed to prepare mesoporous carbon (MC) from macadamia nutshells coated with titanium dioxide nanoparticles (TiO2 NPs) using a hydrothermal method to remove Pb2+ and to test the effectiveness of reusing the lead-loaded spent adsorbent (Pb2+-MC/TiO2 NP nanocomposite) in blood fingerprint detection. The samples were characterized using SEM, which confirmed spherical and flower-like structures of the nanomaterials, whereas TEM confirmed a particle size of 5 nm. The presence of functional groups such as C and Ti and a crystalline size of 4 nm were confirmed by FTIR and XRD, respectively. The surface area of 1283.822 m2/g for the MC/TiO2 NP nanocomposite was examined by BET. The removal of Pb2+ at pH 4 and the dosage of 1.6 g/L with the highest percentage removal of 98% were analyzed by ICP-OES. The Langmuir isotherm model best fit the experimental data, and the maximum adsorption capacity of the MC/TiO2 NP nanocomposite was 168.919 mg/g. The adsorption followed the pseudo-second-order kinetic model. The ΔH° (-54.783) represented the exothermic nature, and ΔG° (-0.133 to -4.743) indicated that the adsorption process is spontaneous. In the blood fingerprint detection, the fingerprint details were more visible after applying the Pb2+-MC/TiO2 NP nanocomposite than before the application. The reuse application experiments showed that the Pb2+-MC/TiO2 NP nanocomposite might be a useful alternative material for blood fingerprint enhancement when applied on nonporous surfaces, eliminating secondary pollution.

Coal Fly Ash Decorated with Graphene and Polyaniline Nanocomposites for Effective Adsorption of Hexavalent Chromium and Its Reuse for Photocatalysis.

Coal fly ash was functionalized and modified with graphene oxide and polyaniline (CFA/GO/PANI nanocomposite) through hydrothermal synthesis, which was used for remediation of hexavalent chromium (Cr(VI)) ions. Batch adsorption experiments were carried out to investigate the effects of adsorbent dosage, pH, and contact time on the removal of Cr(VI). The ideal pH for this work was 2, and it was used for all other studies. The Cr(VI)-loaded spent adsorbent CFA/GO/PANI + Cr(VI) was reused as a photocatalyst for the degradation of bisphenol A (BPA). The CFA/GO/PANI nanocomposite removed Cr(VI) ions rapidly. The adsorption process was best described by pseudo-second-order kinetics and the Freundlich isotherm model. The CFA/GO/PANI nanocomposite demonstrated a high adsorption capacity of 124.72 mg/g for Cr(VI) removal. In addition, the Cr(VI)-loaded spent adsorbent played a significant role in the photocatalytic degradation of BPA with 86% degradation. The reuse of the Cr(VI)-loaded spent adsorbent as a photocatalyst presents a new solution for the reduction of secondary waste from the adsorption process.

Novel development of zinc oxide-coated carbon nanoparticles from pineapple leaves using sol gel method for optimal adsorption of Cu2+ and reuse in latent fingerprint application.

This study underlines a latest approach of preparing nitrogen carbon nanoparticles fused on zinc oxide nanoparticle nanocomposite (N-CNPs/ZnONP nanocomposite) for the uptake of copper ions (Cu2+) from wastewater using a sol gel method. The metal loaded adsorbent was then applied in the latent fingerprint application. N-CNPs/ZnONP nanocomposite proved to be a good sorbent for the optimal adsorption of Cu2+ at pH 8 and 1.0 g/L dosage. Langmuir isotherm best fitted the process with the maximum adsorption capacity of 285.71 mg/g that was superior to most values reported in other studies for the removal of Cu2+. At 25 °C, the adsorption was spontaneous and endothermic. Furthermore, Cu2+-N-CNPs/ZnONP nanocomposite revealed to be sensitive and selective for latent fingerprint (LFP) identification on a variety of porous surfaces. As a result, it is an excellent identifying chemical for latent fingerprint recognition in forensic science.

Polyaniline nanofibers, a nanostructured conducting polymer for the remediation of Methyl orange dye from aqueous solutions in fixed-bed column studies.

Polyaniline nanofibers (PANI NFs) were synthesized and employed as potential adsorbents in a continuous flow fixed-bed column adsorption study for an organic dye, Methyl Orange (MO) removal from water. These nanostructured adsorbents were characterized using ATR-FTIR, FE-SEM, HR-TEM, TGA, BET, XRD, XPS, and the Zeta-sizer. Morphological representations from SEM and TEM analyses showed that the fibers were nanosized with diameters lower than 80 nm and an interconnected network possessing a smooth surface. The SBET of the PANI NFs was found to be 35.80 m2/g. The impact of column design parameters for instance; influent concentration, flow rate, and bed mass was investigated using pH 4 influent MO solutions optimized through batch studies. The best influent concentration, bed length, and flow rate for this study were determined as 25 mg/L, 9 cm (6 g), and 3 mL/min, respectively. The column information was fitted in Thomas, Yoon-Nelson, and Bohart-Adams models. It appeared that the Thomas and Yoon-Nelson models described the data satisfactorily. The PANI NFs were able to treat 29.16 L of 25 mg/L MO solution at 9 cm bed length. A sulfate peak in a de-convoluted sulfur spectrum using XPS verified the successful adsorption of Methyl Orange.

Coal Fly Ash Decorated with Graphene Oxide-Tungsten Oxide Nanocomposite for Rapid Removal of Pb2+ Ions and Reuse of Spent Adsorbent for Photocatalytic Degradation of Acetaminophen.

Coal fly ash was decorated with a graphene oxide-tungsten oxide nanorods nanocomposite (CFA/GO/WO3NRs nanocomposite) via a hydrothermal method and applied for the remediation of lead (Pb2+ ions). The Pb2+ ion-loaded spent adsorbent (CFA/GO/WO3NRs + Pb2+ nanocomposite) was reused for the photodegradation of acetaminophen. CFA/GO/WO3NRs + Pb2+ nanocomposite displayed rapid removal of Pb2+ ions. Pseudo-second-order kinetics and the Langmuir isotherm model described the adsorption data. The adsorption capacity of the CFA/GO/WO3NRs nanocomposite was 41.51 mg/g for the removal of Pb2+ ions. Additionally, the Pb2+ ion-loaded spent adsorbent significantly influenced the degradation of acetaminophen by photocatalysis where 93% degradation was observed. It is worthy to note the reuse application of Pb2+ ion-loaded spent adsorbent as a photocatalyst, which will significantly reduce the secondary waste obtained from conventional adsorption methods.

Self-Assembled Silver Nanoparticles Decorated on Exfoliated Graphitic Carbon Nitride/Carbon Sphere Nanocomposites as a Novel Catalyst for Catalytic Reduction of Cr(VI) to Cr(III) from Wastewater and Reuse for Photocatalytic Applications.

Silver nanoparticles decorated on an exfoliated graphitic carbon nitride/carbon sphere (AgNP/Eg-C3N4/CS) nanocomposites were synthesized by an adsorption method with a self-assembled process. These nanoparticles were characterized by different techniques like UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Raman spectroscopy, scanning electron spectroscopy (SEM), transmission electron spectroscopy (TEM), electrochemical impedance spectroscopy (EIS), and ζ potential. AgNP/Eg-C3N4/CS nanocomposites showed a higher catalytic reduction activity for the conversion of Cr(VI) into Cr(III) with formic acid (FA) at 45 °C when compared to bulk graphitic carbon nitride (Bg-C3N4, Eg-C3N4, CS, and Eg-C3N4/CS). The kinetic rate constants were determined as a function of catalyst dosage, concentration of Cr(VI), pH, and temperature for the AgNP/Eg-C3N4/CS nanocomposite. This material showed higher reduction efficiency (98.5%, k = 0.0621 min-1) with turnover frequency (0.0158 min-1) for the reduction of Cr(VI) to Cr(III). It also showed great selectivity and high stability after six repeated cycles (98.5%). Further, the reusability of the Cr(III)-AgNP/Eg-C3N4/CS nanocomposite was also investigated for the photocatalytic degradation of methylene blue (MB) under visible light irradiation with various time intervals and it showed good degradation efficiency (α = 97.95%). From these results, the AgNP/Eg-C3N4/CS nanocomposite demonstrated higher catalytic activity, improved environmental friendliness, lower cost for the conversion of toxic Cr(VI) to Cr(III) in solutions, and also good reusability.

Polyaniline-Coated TiO2 Nanorods for Photocatalytic Degradation of Bisphenol A in Water.

Polyaniline (PANI)-wrapped TiO2 nanorods (PANI/TiO2), obtained through the oxidative polymerization of aniline at the surface of hydrothermally presynthesized TiO2 nanorods, were evaluated as photocatalysts for the degradation of Bisphenol A (BPA). Fourier-transform infrared spectroscopy analysis revealed the successful incorporation of PANI into TiO2 by the appearance of peaks at 1577 and 1502 cm-1 that are due to the C=C and C-N stretch of the benzenoid or quinoid ring in PANI. Brunauer-Emmett-Teller analysis revealed that PANI/TiO2 had almost double the surface area of TiO2 (44.8999 m2/g vs 28.2179 m2/g). Transmission electron microscopy (TEM) analysis showed that TiO2 nanorods with different diameters were synthesized. The TEM analysis showed that a thin layer of PANI wrapped the TiO2 nanorods. X-ray photon spectroscopy survey scan of the PANI/TiO2 nanocomposite revealed the presence of C, O, Ti, and N. Photocatalytic activity evaluation under UV radiation through the effect of key parameters, including pH, contact time, dosage, and initial concentration of BPA, was carried out in batch studies. Within 80 min, 99.7% of 5 ppm BPA was attained using the 0.2 g/L PANI/TiO2 photocatalyst at pH 10. The quantum yield (QY) of these photocatalysts was evaluated to be 9.86 × 10-5 molecules/photon and 2.82 × 10-5 molecules/photon for PANI/TiO2 and TiO2, respectively. PANI/TiO2 showed better performance than as-synthesized TiO2 with a rate constant of 4.46 × 10-2 min-1 compared to 2.18 × 10-2 min-1. The rate of degradation of PANI/TiO2 was also superior to that of TiO2 (150 mmol/g/h vs 74.89 mmol/g/h). Nitrate ions increased the rate of degradation of BPA, while humic acid consistently inhibited the degradation of BPA. LC-MS analysis identified degradation products with m/z 213.1, 135.1, and 93.1. The PANI/TiO2 nanocomposite was reused up to five cycles with a removal of at least 80% in the fifth cycle. LC-MS results revealed three possible BPA degradation intermediates. LC-MS analysis identified degradation products which included protonated BPA, [C14H13O2 +], and [C9H11O+]. The PANI/TiO2 nanocomposite demonstrated superior photocatalytic activity with respect to improved QY and figure of merit and lower energy consumption.

Spectroscopic characterization and antimicrobial activity of nanoparticle doped cyclodextrin polyurethane bionanosponge.

This study reports on the spectroscopic characterization and antimicrobial potency of polyurethane cyclodextrin co-polymerized phosphorylated multiwalled carbon nanotube-doped Ag-TiO2 nanoparticle (pMWCNT-CD/Ag-TiO2) bionanosponge nanocomposite. The synthesis of pMWCNT-CD/Ag-TiO2 bionanosponge nanocomposite was carried out through the combined processes of amidation and polymerization reactions as well as the sol-gel method. The native nanosponge cyclodextrin and phosphorylated multiwalled carbon nanotube-nanosponge CD (pMWCNT-CD) polyurethanes were also prepared, and their antimicrobial activities carried out for comparison purposes. The synthesized bionanosponge polyurethane materials were characterized using Fourier-transform infrared (FTIR) spectroscopy, Laser Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to give clear information regarding their structural, and dynamic physicochemical properties. The potency tests of the synthesized compounds were carried out against three bacterial strains Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and two fungal representatives Aspergillus ochraceus and Aspergillus fumigatus, using the disc diffusion method. Micro dilution and agar plating were used to determine the minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC), respectively. The results obtained revealed that pMWCNT-CD/Ag-TiO2 exhibits superior antibacterial and antifungal activities when compared to the other bionanosponge polymers tested. Thus, the bionanosponge polyurethane pMWCNT-CD/Ag-TiO2 nanocomposite can be considered as an active antimicrobial compound (AMC).

Dicarboxylic acid cross-linked metal ion decorated bentonite clay and chitosan for fluoride removal studies.

This study focused on the synthesis of a dicarboxylic acid (malic acid (A)), metal ion decorated bentonite clay (BC) modified with chitosan (CS) and the investigation of its defluoridation efficiency in fluoride contaminated groundwater. The synthesized adsorbent showed a fluoride removal capacity of 9.87 mg g-1. Batch adsorption studies were conducted to establish the effect of various parameters such as contact time, pH, initial concentration, and competitor ions. The adsorption isotherms of Freundlich, Dubinin-Radushkevich, and Langmuir were studied and the Freundlich isotherm fitted the data well. Kinetic studies showed that the adsorption process follows pseudo second order kinetics. Thermodynamic studies revealed that the fluoride adsorption process is spontaneous and endothermic. Reuse and regeneration studies were executed for effective application of the nanocomposite. The synthesized adsorbent also has potential for real water treatment applications.

Synthesis of gold nanoparticles using Crinum macowanii bulb extracts and the application of these materials in blood detections at crime scenes.

We here in report the synthesis of gold nanoparticles (AuNPs) using a Crinum macowanii bulb water extract. The as-synthesized AuNPs were characterized using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and a zeta potential-sizer. The results showed that the as-synthesized AuNPs were crystalline and mostly spherical in shape with a small mixture of triangular, tetrahedral, hexagonal, octagonal, and diamond shapes. The as-synthesized AuNPs together with those synthesized by conventional methods were subsequently used as enhancers for the luminol signal in blood detection. It was noted that the AuNPs synthesized from the Crinum macowanii bulb water extract could enhance the chemiluminescence signal for blood detection by luminol to the same extent as AuNPs prepared by conventional methods. Furthermore, both types of AuNPs served as fluorescence enhancers for blood detection when luminol was replaced with the bulb water extract.

Carboxymethyl cellulose thiol-imprinted polymers: Synthesis, characterization and selective Hg(II) adsorption.

Sulfur containing ion imprinted polymers (S-IIPs) were applied for the uptake of Hg(II) from aqueous solution. Cysteamine which was used as the ligand for Hg(II) complexation, was grafted along the epichlorohydrin crosslinked carboxylated carboxymethyl cellulose polymer chain through an amide reaction. The adsorption ability of S-IIPs towards Hg(II) was investigated by kinetic and isotherm models, which, corresponding, showed that the adsorption process followed a pseudo-second-order, fitted well with the Langmuir isotherm with a maximum adsorption capacity of 80 mg/g. Moreover, thermodynamic studies indicated an endothermic and spontaneous reaction with the tendency of an enhanced randomness at the surface of the S-IIPs with temperature increases. S-IIPs indicated a high degree of selectivity towards Hg(II) in the presence of Cu2+, Zn2+, Co2+, Pb2+ and Cd2+. Furthermore, the efficiency of S-IIPs was also evaluated against real samples showing 86.78%, 91.88%, and 99.10% recovery for Hg(II) wastewater, ground water and tap water, respectively. In this study, the adsorbent was successfully regenerated for five cycles, which allows for their reuse without significant loss of initial adsorption capability.

Synthesis of N-doped ZnO nanoparticles with cabbage morphology as a catalyst for the efficient photocatalytic degradation of methylene blue under UV and visible light.

In this study, the synthesis of nitrogen-doped zinc oxide nanoparticles with a cabbage like morphology (N-ZnONCBs) by a hydrothermal method using zinc acetate dihydrate as a precursor and hydrazine monohydrate as a nitrogen source is reported. N-ZnONCB were characterized using UV-visible Spectroscopy (UV-Vis), Fluorescence Spectroscopy, Fourier Transmittance Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), Raman Spectroscopy, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Dispersive Spectroscopy (EDS) and EDX elemental mapping. N-ZnONCBs were tested for their photocatalytic capabilities in the degradation of methylene blue (MB) under UV-light and visible light irradiation for about 0 to 80 minutes and 0 to 50 min respectively. The N-ZnONCB catalyst demonstrated improved photodegradation efficiency (98.6% and 96.2%) and kinetic degradation rates of MB (k = -0.0579 min-1 and k = -0.0585 min-1) under UV light and visible light irradiation at different time intervals. The photodegradation study was also evaluated with different dosages of N-ZnONCB catalyst, different initial concentrations of MB and variation in the pH (3, 5, 9 and 11) of the solution of MB under UV light and visible light irradiation. The photocatalytic degradation intermediate products were obtained by liquid chromatography mass spectra (LC-MS) and also complete mineralization was determined by using Total Organic Carbon (TOC) studies. This photocatalyst was also tested with 2,4-dichlorophenol (2,4-DCP) under visible light irradiation at different time intervals. Fluorescence and quenching studies were performed for the binding interaction between the N-ZnONCB catalyst and MB dye. A Zetasizer was used to find the charge and average size of the N-ZnONCB catalyst and also the charge of the N-ZnONCB catalyst before and after MB dye solution adsorption. The N-ZnONCB catalyst was also tested for its photostability and reusability with a percentage degradation rate of MB (93.2%) after 4 cycle experiments. These results have clearly demonstrated that the N-ZnONCB catalyst can be applied for the photocatalytic degradation of MB from wastewater samples.

Hydrous CeO2-Fe3O4 decorated polyaniline fibers nanocomposite for effective defluoridation of drinking water.

Hydrous CeO2-Fe3O4 (HCeFe) decorated polyaniline nanofibers (HCeFe NFs) were obtained through a simple co-precipitation deposition approach on pre-synthesized polyaniline nano-fibers (PANI NFs), and evaluated as adsorbents for fluoride removal from synthetic and real water samples. Field emission scanning electron microscopy/energy dispersive X-ray spectroscopy (FE-SEM/EDS), high resolution-transmission electron microscopy (HR-TEM), Braunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric-differential thermal analysis (TGA-DTA), X-ray photoelectron spectroscopy (XPS) and dynamic mechanical analysis (DMA) techniques were used to characterize the hybrid nanomaterials. The optimised HCeFe NFs adsorbent with specific surface area 66 m2/g, exhibited excellent adsorption efficiency towards fluoride ions (F-) via both electrostatic interactions and ion exchange mechanisms. F- adsorption followed the pseudo-second-order rate model and best fitted the Langmuir isotherm, with the maximum capacities within 93.46-117.64 mg/g over a broad pH range 3-10, respectively. The determined thermodynamic parameters, including enthalpy (ΔH°â€¯- 15.1 kJ/mol) and Gibbs free energies change (ΔG°â€¯< 0) indicated to the exothermic and a spontaneous nature of the sorption process. The regeneration of HCeFe NFs showed a considerable adsorption-desorption efficiency over three consecutive cycles. Ultimately, the adsorbent was tested on spiked F- containing groundwater and the obtained results demonstrated its potential utility for defluoridation of natural water.

Removal of cobalt and lead ions from wastewater samples using an insoluble nanosponge biopolymer composite: adsorption isotherm, kinetic, thermodynamic, and regeneration studies.

In this study, an insoluble nanosponge biopolymer composite was synthesized, using a combined process of amidation reaction, cross-linking polymerization, and sol-gel method to obtain a phosphorylated multiwalled carbon nanotube-cyclodextrin/silver-doped titania (pMWCNT-ßCD/TiO2-Ag). This work mainly emphasized on the removal of lead (Pb2+) and cobalt (Co2+) metal ions from synthetic and real wastewater samples using the synthesized pMWCNT-ßCD/TiO2-Ag as a biosorbent. The new material was characterized by Fourier transform infrared (FTIR) spectroscopy, zeta potential, Brunauer-Emmett-Teller (BET) method, and scanning electron microscopy (SEM). Adsorption studies for the model pollutants were performed in batch mode. The effect of the solution pH, adsorbent dosage and the presence of competiting ions were investigated. The isotherm, kinetic, thermodynamic, and regeneration studies were also undertaken. The ability of the new material to effectively remove Pb2+ and Co2+ from synthetic wastewater and mine effluent samples was tested. The maximum removal capacities achieved for the removal of Pb2+ and Co2+ from mine effluent sample were 35.86 and 7.812 mg/g, respectively.

Ultrasound assisted adsorptive removal of hazardous dye Safranin O from aqueous solution using crosslinked graphene oxide-chitosan (GOCH) composite and optimization by response surface methodology (RSM) approach.

Chitosan (CH) was crosslinked with graphene oxide (GO) by combining solutions of CH and GO. Characterisations by ATR-FTIR, FE-SEM and XRD confirmed the formation of the GOCH composite. Removal of the dye Safranin Orange (SO) by ultrasonic adsorption from aqueous solution was tested by the composite. The removal of the cationic dye was more favourable at pH values greater than 5.2 and the optimum pH was found to be 6.5. The adsorption kinetics followed a pseudo-first order model and the rate-limiting step was identified as boundary layer diffusion from the Intraparticle diffusion model. The sonication assisted adsorption kinetic data were compared with the non-sonicated one and it was found that sonication has a marked effect on the adsorption kinetics. The Redlich Peterson adsorption isotherm described the adsorption with more resemblance to the Langmuir Model than the Freundlich Model suggesting that monolayer adsorption predominated. From Response Surface Methodology it was noted that the combined effect of pH and initial concentration was antagonistic while that of sonication time was synergistic. The optimum parameters from the RSM model were found to be pH 6.82, initial SO concentration 425mgL-1 and sonication time 25min. This was in good agreement with the experimental results.

Hydrous ZrO2 decorated polyaniline nanofibres: Synthesis, characterization and application as an efficient adsorbent for water defluoridation.

A new hybrid material comprising hydrous zirconium oxide (HZrO2) supported onto polyaniline (PANI) nanofibres (HZrO2@PANI NFs) was prepared via the precipitation of HZrO2 onto as-synthesized PANI NFs and tested for its defluoridation capabilities. The developed adsorbent (HZrO2@PANI NFs) was fully characterized by FTIR, BET, XRD, SEM-EDX, TEM-(S)TEM, XPS, and zeta potential measurements. HZrO2@PANI NFs achieved 2-fold BET surface area ∼86.64 m2/gas compared to PANI NFs ∼44.72 m2/g, implying that the incorporation of HZrO2 onto the PANI nanofibres enhanced the available surface area for effective fluoride adsorption. Moreover, HZrO2@PANI NFs was found to be effective over a wide pH range (3-9) as designated by its high pHpzc ∼9.8. The adsorption kinetics obeyed the pseudo-second-order model well with equilibrium attainment in 30min. Adsorption isotherm was best described by the Langmuir model and the maximum adsorption capacities obtained were 83.23 and 28.77mg/g at pH 3 and 6.5, respectively, which is superior to most ZrO2 based adsorbents reported in the literature and better than that of native PANI. Furthermore, the developed adsorbent manifested quite a selective fluoride uptake at pH 3 as compared to pH 6.5±0.1 wherein significant chemical affinity competition was presented by phosphate ions followed by bicarbonate and sulfate. The recyclability of HZrO2@PANI NFs for four cycles and its applicability to fluoride spiked ground water has also been demonstrated. The adsorption mechanism was interpreted with the help of FTIR, XPS and Zeta potential analysis and the results revealed the involvement of both anion exchange and electrostatic attraction in the adsorption of F- ions. Thus, a new efficient adsorbent with reasonably high adsorption capacity and superior pH tolerance has been developed for fluoride removal.

Selective removal of toxic Cr(VI) from aqueous solution by adsorption combined with reduction at a magnetic nanocomposite surface.

The adsorption of toxic hexavalent chromium (Cr(VI)) and its reduction to trivalent chromium (Cr(III)) are important processes for the treatment of industrial wastewater. Conducting polymers can adsorb and reduce Cr(VI) to less toxic Cr(III) but have low adsorption capacities due to agglomeration of particles and are difficult to separate from treated water. In this study, magnetic polypyrrole (PPy)-polyaniline (PANI)/iron oxide (Fe3O4) nanocomposite was synthesized for the selective removal of Cr(VI) in aqueous solution. PPy-PANI/Fe3O4 nanocomposite was characterized using various techniques including ATR-FTIR, FE-SEM, HR-TEM, EDX, TGA, XRD, VSM and XPS analyses. PPy-PANI/Fe3O4 nanocomposite (0.05g) removed 99% of Cr(VI) from aqueous solution (100mg/L, pH 2). Speciation studies confirmed Cr(VI) adsorption and reduction to Cr(III) by the PPy-PANI/Fe3O4 nanocomposite in solutions with initial pH of 2 and 3 and that no Cr(VI) reduction occurred at pH values of 4 and above. The Langmuir maximum adsorption capacity for Cr(VI) removal by PPy-PANI/Fe3O4 nanocomposite at pH 2 was 303mg/g at 25°C. PPy-PANI/Fe3O4 nanocomposite was highly selective for Cr(VI) removal and could be used for three consecutive treatment cycles without loss of adsorption capacity. Moreover, the magnetic nanocomposite could be separated from the reaction fluid using an external magnet. PPy-PANI/Fe3O4 nanocomposite is therefore a promising magnetic adsorbent for the treatment of industrial wastewater.

Epichlorohydrin crosslinked carboxymethyl cellulose-ethylenediamine imprinted polymer for the selective uptake of Cr(VI).

A new ion-imprinted polymer (IIP) was synthesized from sodium carboxymethyl cellulose and used for the adsorption of hexavalent chromium from aqueous solution. Epichlorohydrin was used to stabilize the polymer before ethylenediamine (EDA) ligand and Cr(VI) were introduced. The obtained IIP was characterized with FTIR, XPS, TGA,13C NMR, SEM, EDX, BET and zeta sizer. The kinetics of adsorption followed a pseudo-second-order model while the Langmuir adsorption isotherm provided the best fit with a maximum adsorption capacity of 177.62mg/g at 25°C. The Langmuir adsorption capacity for the non-imprinted polymer (NIP) at 25°C was 149.93mg/g. Thermodynamic parameters indicated an endothermic process and spontaneous adsorption of Cr (VI) on the polymers. IIP adsorbent was successfully recycled 5 times using 0.1M NaOH as a leachate; 98% Cr(VI) was desorbed during the last adsorption-desorption cycle.