Dhiraj Sud

Agricultural waste material as potential adsorbent for sequestering heavy metal ions from aqueous solutions : A review

Heavy metal remediation of aqueous streams is of special concern due to recalcitrant and persistency of heavy metals in environment. Conventional treatment technologies for the removal of these toxic heavy metals are not economical and further generate huge quantity of toxic chemical sludge. Biosorption is emerging as a potential alternative to the existing conventional technologies for the removal and/or recovery of metal ions from aqueous solutions. The major advantages of biosorption over conventional treatment methods include: low cost, high efficiency, minimization of chemical or biological sludge, regeneration of biosorbents and possibility of metal recovery. Cellulosic agricultural waste materials are an abundant source for significant metal biosorption. The functional groups present in agricultural waste biomass viz. acetamido, alcoholic, carbonyl, phenolic, amido, amino, sulphydryl groups etc. have affinity for heavy metal ions to form metal complexes or chelates. The mechanism of biosorption process includes chemisorption, complexation, adsorption on surface, diffusion through pores and ion exchange etc. The purpose of this review article is to provide the scattered available information on various aspects of utilization of the agricultural waste materials for heavy metal removal. Agricultural waste material being highly efficient, low cost and renewable source of biomass can be exploited for heavy metal remediation. Further these biosorbents can be modified for better efficiency and multiple reuses to enhance their applicability at industrial scale.

Heterogeneous Photocatalytic Degradation of Selected Organophosphate Pesticides: A Review

This review is an attempt to summarize the research carried out on heterogeneous photocatalytic treatment of selected organophosphates present invariably in shallow and ground water supplies. The basic principle of semiconductor-mediated photocatalytic process, experimental conditions used, optimization of the parameters affecting the efficiency, and degradation mechanism has been explained. The kinetics of organophosphate degradation and the analytical techniques for identification of intermediates have been reviewed. The by-products and intermediates formed along with the proposed pathways for the degradation of various subclasses of organophosphate pesticides are widely discussed.

A greener approach to synthesize visible light responsive nanoporous S-doped TiO2 with enhanced photocatalytic activity

A visible light responsive nanoporous sulfur doped TiO2 nanophotocatalyst was prepared by a greener approach using ultrasonic irradiation. The synthesized product was characterized by physicochemical techniques such as X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The elemental composition, morphology and surface area were determined by Energy Dispersive X-ray Spectroscopy (EDXS), Scanning Electron Microscopy (SEM), and High Resolution Transmission Electron Microscopy (HRTEM), Brunauer–Emmett–Teller (BET) surface area analysis, respectively. The results confirmed the formation of a nanoporous S-doped TiO2 photocatalyst having the anatase phase and exhibiting a particle size of about 8–24 nm. The influence of sulfur doping on the phase transition, band gap and crystalline size of the TiO2 was investigated by varying the molar ratio of titanium and sulfur. Sulfur doping leads to the lowering of the band gap of TiO2 from 3.25 eV to 2.47 eV and also delays the phase transition of TiO2 from the anatase to rutile form. The response of the synthesized catalysts towards the photo-induced degradation of an organic pollutant was investigated in different regions (490 nm, 565 nm and 660 nm) of the solar spectrum using 2-chlorophenol as a model compound. Maximum photocatalytic degradation efficiency was found with S-550 at pH 6 under visible light of 660 nm. The synthesized S-doped TiO2 photocatalyst showed profound improvement in photocatalytic activity under solar light as compared to TiO2 Degussa and TiO2 Merck.

Comparative studies on TiO2/ZnO photocatalyzed degradation of 4-chlorocatechol and bleach mill effluents

Abstract The study presents a comparative account on TiO2 and ZnO facilitated photocatalytic degradation of 4-chlorocatechol (4-CC) typically found in bleach mill effluents (BME). The effect of major process parameters such as catalyst dose, pH, oxidant concentration, and source of light (UV/solar) on degradation efficiency has been investigated. The degradation efficiency of 4-CC was assessed in terms of absorbance as a function of irradiation time. Of the two catalysts screened, ZnO has been observed to be a better catalyst over TiO2. The maximum degradation of 99.2 and 91.6% was obtained with 1.5 g/L ZnO, at pH 8, after 2 h irradiation and with 2.5 g/L TiO2, at free pH (6.5), 0.04 M NaOCl concentration after 6 h irradiation, respectively. Further, the kinetics of degradation process was found to follow pseudo-first-order reaction. The photocatalytic process was applied to treat actual BME and degradation of effluent, observed in terms of chemical oxygen demand reduction, was 36.5 and 39% with UV/TiO2/N...

Modified agricultural waste biomass with enhanced responsive properties for metal-ion remediation: a green approach

Dalbergia sissoo pods, a lignocellulosic nitrogenous waste biomass, was evaluated for sequestering of Cr(VI) from synthetic wastewater. Dalbergia sissoo pods (DSP) were used in three different forms, viz. natural (DSPN), impregnated in the form of hydrated beads (DSPB), and in carbonized form (DSPC) for comparative studies. Batch experiments were performed for the removal of hexavalent chromium. Effects of pH adsorbent dose, initial metal-ion concentration, stirring speed, and contact time were investigated. The removal of metal ions was dependent on the physico-chemical characteristics of the adsorbent, adsorbate concentration, and other studied process parameters. Maximum metal removal for Cr(VI) was observed at pH 2.0. The experimental data were analyzed based on Freundlich and Langmuir adsorption isotherms. Kinetic studies indicated that the adsorption of metal ions followed a pseudo-second-order equation.

Heterostructured TiO2/ZnO–excellent nanophotocatalysts for degradation of organic contaminants in aqueous solution

AbstractHeterostructured ZnO/TiO2 nanophotocatalysts were prepared by precipitation method in molar ratio of 1:9 (ZT9), 1:1(ZT), 9:1(Z9T), and ZnO was also prepared with the same method. The prepared photocatalysts were characterized with X-ray diffraction, scanning electron microscopy, and UV–Vis spectroscopy. The average crystallite size of samples was calculated to be about 20–25 nm. The band gap of ZnO/TiO2 photocatalysts is smaller than that of prepared ZnO (3.70 eV). Their photocatalytic activity was evaluated using acid orange 7 (AO7) as a model organic compound. The rate of decolorization was estimated from residual concentration spectrophotometrically, and mineralization rate was studied by measuring COD. Coupled oxide ZT9 has higher photocatalytic efficiency (81.09%) than ZnO prepared (39.98%), Degussa P25 TiO2 (69.09%) or TiO2 Merck (26.14%) at pH 7. ZT and Z9T have better photocatalytic efficiency than Degussa P25 TiO2 at pH 8. The results clearly indicate that ZT9 is found to be most active i...

Nano sized carbonized waste biomass for heavy metal ion remediation

Abstract Utilization of agricultural waste material with approach to enhance the heavy metal remediation properties by carbonizing the biomass at nano size particles has been explored in present investigation from aqueous solutions. In this study the lignocellulosic, nitrogenous agricultural waste biomass Delbergia sissoo pods (DSP) has been tried for sequestering of Cd (II), Pb (II) and Ni (II) metal ions from aqueous solutions. Batch experiments were performed for removal of targeted metal ions keeping in consideration the preliminary affecting parameters such as effect of adsorption dose, pH, initial metal ion concentration, stirring speed and contact time. The sorption studies were analyzed by using, Freundlic isotherm and Langmuir isotherm models. The kinetics of the process was evaluated by pseudo pseudo-first order and pseudo second order kinetic models. Studies reveal that the equilibrium was achieved with in 30 min of the contact time at optimized parameters. Analytical studies of biosorbent were done by means of FT-IR, SEM and XRD. Desorption experiments were carried out using HCl solution with a view to regenerate the spent adsorbent and to recover the adsorbed metal ions.

Time and temperature dependent sorption behaviour of dimethoate pesticide in various Indian soils

Abstract Experiments were conducted to study the sorption behaviour of dimethoate in three Indian soils at different temperatures. A kinetic study showed that adsorption equilibrium was reached within 15 h at different initial levels of pesticide concentration. Applicability of the pseudo second order kinetic model suggested that the adsorption process was complex and several mechanisms were involved. The Freundlich model explained the adsorption behaviour adequately and the isotherms were of S-type. The adsorption process was found to be strongly affected by temperature. The Gibbs free energy change, ΔGº values (from -15.81 to -16.60 kJ mol-1) indicated that the process was spontaneous and exothermic in nature. The change in enthalpy of adsorption, ΔH° values (from -17.729 to -21.539 kJ mol-1) suggested that relatively weak H-bond forces were the main driving forces for adsorption. Desorption was found to be concentration- and temperature-dependent with higher desorption occurring at higher temperature and concentration levels. The results signify the importance of temperature in controlling the mobility of dimethoate in water bodies.

Ultrasound Assisted Synthesis of Visible Light Responsive Nitrogen Doped TiO2 Nano Photocatalyst

The present study is an attempt to synthesize N-doped TiO2 nanophotocatalyst using sonochemical method, having photocatalytic activity in the visible region. Non-metal doped nanocatalysts have been successfully synthesized and characterized structurally and physiochemically by using XRD, SEM, TEM, EDX, UV-VIS, FT-IR, Raman and PL. The photocatalytic activity of the synthesized photocatalyst was investigated for the degradation of 2-CP as model compound. The result confirms the successful synthesis of N-doped photocatalyst with particle size 34 nm having anatase phase and shows new peak in a visible region at 587 nm..

Chelating Ion Exchangers: Theory and Applications

The lack of selectivity, sensitivity, and capacity of the conventional ion exchange resins particularly for trace heavy metal ions had led to the development of metal-ion-specific exchange resins known as chelating ion exchangers or chelating ion exchange resins. The chelating ion exchangers are the polymers covalently bonded to ligands forming complexes with metal ions through functional groups. The chelating ion exchangers consist essentially of two components – polymeric matrix and chelating ligands. A variety of polymeric matrices, namely, inorganic (silica) and organic – both natural and synthetic [polystyrene divinyl benzene (PS-DVB), polymethacrylate (PMA)] – have been employed for the synthesis of chelating exchangers. Most of the commercially available chelating exchangers are silica- or PS-DVB-based and have diverse applications. A large number of diversified chelating ligands may be employed for the synthesis of chelating exchangers, such as the carbamates, β-diketones, diamine, iminodiacetic acid and amino acids, aldoxime, aminophosphonic acids, various azo-triphenylmethane dyes, and 8-hydroxyl quinolinol. These chelating ligands are incorporated into a polymeric matrix by different methods. The chelation exchange mechanisms are found to be slower than ion exchange, and efficient separations are possible only by the choice of the correct chelating functional group. Furthermore, the chelating ligand should have a broad spectrum of chelating action and have no special selectivity for one or two metal ions. The structure, coordination chemistry, and applications of most commonly employed chelating ion exchangers have been discussed. Chelating ion exchangers containing iminodiacetic acid (IDA) chelating group have been the most studied for metal separations. The efficiency and versatility of another chelating exchanger containing the chelating ligand aminophosphonate have been addressed. The development of new chelating ion exchange materials with special chelating properties can provide better kinetics of interaction between metal ion and chelating groups, and better understanding of their coordination chemistry for surfaces can revolutionized the domain of chromatographic separations and analysis of trace metal ions particularly from complex matrices.