Jane Catherine Ngila

Effect of functionalization on the adsorption capacity of cellulose for the removal of methyl violet

In this research paper a comparative study has been carried out for the removal of methyl violet dye using unfunctionalized and functionalized cellulose. The functionalization was achieved through esterification of cellulose with furan-2,5-dione. The functionalization of the cellulose was evidenced using BET, FT-IR, SEM and TGA. The adsorption isotherm data was fitted using different isotherm models like Langmuir, Freundlich, Temkin, Flory-Huggins and Dubinin-Kaganer-Radushkevich models and found to follow Langmuir and Temkin isotherm models with high value of correlation coefficients. Functionalized cellulose (106.38 mg g(-1)) showed higher dye removal capability than unfunctionalized cellulose (43.668 mg g(-1)). The kinetics of adsorption was investigated using pseudo first order, second order, Elovich, liquid film diffusion and intra-particle diffusion models. The mechanism of adsorption was found to follow pseudo second order rate equation. Thermodynamic studies showed that the adsorption process was endothermic and spontaneous.

Efficient removal of rhodamine 6G dye from aqueous solution using nickel sulphide incorporated polyacrylamide grafted gum karaya bionanocomposite hydrogel

This research paper reports the synthesis and usage of the polyacrylamide (PAAm) grafted gum karaya (Gk) and nickel sulphide nanoparticle based hydrogel to effectively remove rhodamine 6G dye (R6G) from aqueous solution. Initially, the hydrogel polymer of the Gk with the PAAm was synthesized using the graft co-polymerization technique. In the second step, the nickel sulphide nanoparticles were incorporated in situ within the hydrogel polymer matrix. The synthesized hydrogel nanocomposite was characterized using different characterization techniques such as XRD, FTIR, SEM, and TEM. The changes in the surface area, pore volume and pore diameter after the incorporation of nanoparticles were studied using the BET technique. The adsorption of R6G onto the hydrogel nanocomposite followed the Langmuir adsorption isotherm with a maximum adsorption capacity of 1244.71 mg g−1. The adsorption kinetics followed the pseudo-second order rate model. Furthermore, various thermodynamic parameters such as ΔS°, ΔH° and ΔG° were calculated to check the spontaneity and nature of the process of adsorption. The hydrogel nanocomposite was used for five successive cycles of adsorption–desorption. Therefore, the nanocomposite hydrogels have proved their potential for the removal of cationic dyes from aqueous solutions.

Morphogenesis of ZnO nanostructures: role of acetate (COOH−) and nitrate (NO3−) ligand donors from zinc salt precursors in synthesis and morphology dependent photocatalytic properties

We have studied the anion ratio effect of acetate and nitrate ions on the formation of different morphologies of ZnO crystals in the presence of NaOH and HMTA. We have varied the concentration of zinc salt precursors as well as adopted three different methods of synthesis (chemical, ultrasonic and hydrothermal) to study their effects on the size/shape of the formed ZnO nanostructures. We found that these anions which spontaneously get introduced along with zinc salt can modify the structure depending on their ratio. The photocatalytic properties of the as obtained ZnO nanostructures (nanoflower, nanospindle and nanorod) were tested towards anionic dye methyl orange. The results show that rod like ZnO nanostructures are catalytically more reactive than nanoflowers and nanospindles. Based on these results we propose that selection of appropriate zinc salt is important to rationally design experiments for a particular morphology. Furthermore, it is also suggested that the role of other precursor salts in synergy will lead to the formation of various nanostructures and this can be extended to other metal oxides of interest for modification.

Photoelectrochemical degradation of orange II dye in wastewater at a silver–zinc oxide/reduced graphene oxide nanocomposite photoanode

In the search for novel and efficient electrochemical materials as electrodes for photoelectrochemical degradation and mineralisation of organic pollutants in water treatment, a photoanode consisting of a composite of silver (Ag), zinc oxide (ZnO) and reduced graphene oxide (rGO) was synthesized, characterised and photoelectrochemically applied in the degradation and possible mineralisation of organic pollutants in a water treatment process. The ZnO and Ag–ZnO nanoparticles were synthesised by a facile one-step co-precipitation method followed by calcination at 400 °C. The nanoparticles were further used to dope reduced graphene oxide by dispersion in methanol, sonicated and dried. The prepared materials were characterised using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The obtained Ag–ZnO–rGO nanocomposite was compressed and fabricated into an electrode. The photoelectrochemical applicability of Ag–ZnO–rGO as a photoanode material was tested by the photoelectrochemical degradation of orange II dye as target organic pollutant in 0.1 M Na2SO4 solution at a current density of 15 mA cm−2. The results revealed that the photoelectrochemical process was pH and current density dependent and that the Ag–ZnO–rGO electrode has a higher photoelectrochemical performance (93% removal efficiency) compared to the ZnO–rGO electrode (87% removal efficiency) and rGO (73% removal efficiency). The degree of mineralisation of the dye was determined using total organic carbon (TOC) measurement which gave better removal efficiency for the Ag–ZnO–rGO electrode (67.9%) in relation to ZnO–rGO (58.7%) and rGO (45.3%) electrodes.

Characterization and stability of TiO2 nanoparticles in industrial dye stuff effluent

ABSTRACT Stability studies were conducted in different solutions (deionized water (DI), NaCl, CaCl2, and MgCl2) at different pH. Agglomeration and zeta potential were influenced by ionic strength, type of electrolyte, and the presence of dye stuff. The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was used to analyze the stability and/or agglomeration of the nanoparticles in the different solutions. Repulsive or attractive forces stipulated by the DLVO theory were used to quantitatively discuss the results. The increase in ionic strength increased agglomeration which was linked to pHpzc, as there were minimal electrostatic repulsions at the pzc, yet the attractive van der Waals forces were dominant. Addition of the dye stuff significantly decreased the agglomeration as the dye stuff changed the overall zeta potential of TiO2 nanoparticles to negative across the entire pH which improved stability as there were particle–particle repulsions. Monovalent and divalent cations were compared and Ca2+ increased the mean diameter of nanoparticles as it effectively decreased the EDL of the nanoparticles, thus enhancing agglomeration. The DLVO theory was successful at explaining, in terms of the interaction energies between nanoparticles, the phenomena that caused either agglomeration or stability of the as-synthesized TiO2 nanoparticles in the different solutions. GRAPHICAL ABSTRACT

A novel approach to low-temperature synthesis of cubic HfO 2 nanostructures and their cytotoxicity

The development of a strategy to stabilise the cubic phase of HfO2 at lower temperatures is necessary for the emergence of unique properties that are not realised in the thermodynamically stable monoclinic phase. A very high temperature (>2600 °C) is required to produce the cubic phase of HfO2, whereas the monoclinic phase is stable at low temperature. Here, a novel rapid synthesis strategy was designed to develop highly crystalline, pure cubic-phase HfO2 nanoparticles (size <10 nm) using microwave irradiation. Furthermore, the as-prepared nanoparticles were converted to different morphologies (spherical nanoparticles and nanoplates) without compromising the cubic phase by employing a post-hydrothermal treatment in the presence of surface modifiers. The cytotoxicities and proliferative profiles of the synthesised cubic HfO2 nanostructures were investigated over the MCF-7 breast cancer cell line, along with caspase-3/7 activities. The low-temperature phase stabilisation was significantly attributed to surface imperfections (defects and deformations) induced in the crystal lattice by the desirable presence of Na2S·xH2O and NaOH. Our work provides unprecedented insight into the stabilisation of nanoscale cubic-phase HfO2 in ambient environments; the method could be extended to other challenging phases of nanomaterials.

Ionic liquid-assisted synthesis of Ag/Ag2Te nanocrystals via a hydrothermal route for enhanced photocatalytic performance

Herein, Ag2Te and Ag/Ag2Te nanocrystals were synthesised via a hydrothermal method using diphenyl ditelluride as a new tellurium source and 1-butyl-3-methyl imidazolium acetate (BMIA IL) as a structure controlling and conducting coating source. The as-synthesized nanocrystals were characterized via XRD, SEM-EDS, XPS, TEM, FTIR, UV-vis, and PL measurements. The photocatalytic behaviour of the Ag2Te and Ag/Ag2Te nanocrystals was investigated for the degradation of methylene blue in the presence of UV-visible light. After 90 minutes of photo-irradiation, up to 95.74% of the dye was photocatalytically degraded by the Ag/Ag2Te nanocrystals. This improved photocatalytic activity was achieved due to the effective charge separation, synergic effect of the Ag2Te semiconductor and plasmonic metallic Ag, conducting BMIA IL coating, and morphological features of the nanocrystals. The appearance of strong peaks in the photoluminescence emission spectra at room temperature suggests a high-level transition in the prepared plasmonic photocatalyst system. The enhanced photocatalytic mechanism for dye degradation using the Ag/Ag2Te nanocrystals has also been described. Thus, the present report presents new insight into the design and development of Ag/Ag2Te plasmonic photocatalysts for environmental applications.

Remediation of Some Selected Heavy Metals from Water Using Modified and Unmodified Mushrooms

The dispersal of toxic heavy metals by water from natural and anthropogenic is a worldwide environmental concern due to pollution. Despite some metals playing an important role in body, they are toxic when the level exceeds the tolerance limits while others such as lead have no known physiological value to human beings. Since heavy metals cannot be degraded, then their removal from drinking water is necessary. Mushrooms are readily available in Bomet County and their metal removal ability was investigated. The study aimed at removing heavy metals from water by adsorption using mushroom, as a cost-effective and sustainable method. The raw mushroom was modified with sodium hydroxide and characterization of both the parent material and its modified form was done using Fourier Transform Infrared spectrometry (FTIR). Sorption experiments were carried out using the batch adsorption method and sorption parameters including pH, contact time, adsorbent dose and initial metal ion concentration investigated. The results found out that the sorption capacity for cadmium ions ranged from 1.826- 25.285 mg/g by the unmodified edible mushroom (UEM), the modified edible mushroom (EM), unmodified toxic mushroom (UTM) and modified toxic mushroom (TM). For copper ions, sorption capacity ranged from 0.002-4.097 mg/g, while that of the lead ions ranged from 1.345-2.593 mg/g by the UEM, EM, UTM and TM respectively. The sorption capacity showed improvement on modification as sorption of cadmium increased from 1.826-25.285 mg/g by the UEM, EM, UTM and TM. At a pH range of 4-6, the sorbent material was found to remove up to 90% of the metals. The sorbent material had a removal efficiency of 95% of the metals in less than 20 minutes. The UEM and UTM fitted well in Langmuir adsorption isotherm model for cadmium and lead ions. For copper ions, UEM, EM, UTM and TM fitted in the Freundlich model. TM for lead ions best fitted in the Freundlich model. The bio-sorption kinetics was determined by fitting first-order-Lagergreg and Pseudo-second-order kinetics models to the experimental data. It was found that the data for lead was better described by the pseudo-second-order model. For copper ion, the data was best described by Ho’s pseudo second order for UEM and UTM, cadmium ions for all sorbents was best described by Lagergreg’s first-order kinetics. The FTIR analysis suggested the possibility of the participation of carboxyl groups in metal uptake. The levels of dissolved organic carbon (DOC) were found to be 19.0 mg/L in the raw material and 2.19 mg/L after modification. It was confirmed that modification minimized secondary pollution. This indicated that mushrooms have a potential application for the remediation of metal polluted waters.

Gold nanoparticles for the quantification of very low levels of poly-diallyldimethylammonium chloride in river water

We present a colorimetric method based on gold nanoparticle aggregation to detect and quantify poly-diallyldimethylammonium chloride (poly-DADMAC), a common water treatment polyelectrolyte, in river water. The protocol developed has an excellent linear range between 10 and 100 μg L−1 (R = 0.99), with a lower limit of detection of 0.54 μg L−1 and a lower limit of quantification of 1.5 μg L−1. The method has excellent intermediate precision (0.1–0.7%), relatively quick analysis times, requires no extraction or derivatization methods, and is robust and rugged. Results of spiked river water samples collected from the Umgeni River located in the province of KwaZulu-Natal, South Africa show that the method can detect low levels of poly-DADMAC in environmental matrices.

Design Technology for Bioenergy Conversion of Organic Fraction of Municipal Solid Waste

In this study, we investigated the use of a laboratory batch anaerobic digester technology, for biochemical methane potential (BMP) and the bioenergy process design from anaerobic co-digestion of different organics fraction of municipal solid waste (OFMSW) originating from the city’s landfills. The carbon-to-nitrogen (C/N) ratio of OFMSW was found to be below 13. Through co-digestion, the C/N ratio settled at 14. Laboratory experimental data from 500 ml batch anaerobic digester operating at mesophilic temperature of 37 °C and pH of 7 had good productivity of methane of average 59.49% with (54–62%) recommended in the literature and was used to derive volume of digester and surface area. Via the application of the simple multi-attribute rating (SMART) technique of multiple-criteria decision analysis (MCDA) as a decision support tool, the most preferred model option for bioenergy design technology was selected from a list of potential alternatives available in the market. The geometry of the biodigester parameters was comparable with the process.