Vinod Kumar Gupta

Chemical treatment technologies for waste-water recycling—an overview

The global population is increasing and because of this, the world may experience great fresh water scarcity. Our water resources are limited and, hence, water treatment and recycling methods are the only alternatives for getting fresh water in the coming decades. Therefore, there is a great need for the development of a suitable, inexpensive and rapid wastewater treatment techniques and reuse or conservation methods in the present century. The different types of water treatment and recycling techniques have been discussed in terms of their basic principles, applications, costs, maintenance and suitability. Additionally, a systematic approach to water treatment and recycling involving their understanding, evaluation and selection parameters has been presented. A brief guideline for the selection of the appropriate technologies for specific applications has been evaluated. This review adds to the global discussions on water scarcity solutions.

Advances in water treatment by adsorption technology

Among various water purification and recycling technologies, adsorption is a fast, inexpensive and universal method. The development of low-cost adsorbents has led to the rapid growth of research interests in this field. The present protocol describes salient features of adsorption and details experimental methodologies for the development and characterization of low-cost adsorbents, water treatment and recycling using adsorption technology including batch processes and column operations. The protocol describes the development of inexpensive adsorbents from waste materials, which takes only 1–2 days, and an adsorption process taking 15–120 min for the removal of pollutants. The applications of batch and column processes are discussed, along with suggestions to make this technology more popular and applicable.

Adsorptive removal of dyes from aqueous solution onto carbon nanotubes: a review.

Adsorption is a widely used technique for the separation and removal of pollutants from wastewaters. Carbon nanotubes (CNTs) are emerging as potential adsorbents because of its well defined cylindrical hollow structure, large surface area, high aspect ratios, hydrophobic wall and easily modified surfaces. In this review, dye adsorption capability of CNTs and CNT based composites from aqueous system has been compiled. This article provides the information about the defect, adsorption sites on CNTs and batch adsorption studies under the influence of various operational parameters such as contact time, solution pH, temperatures etc. and deals with mechanisms involved in adsorption of dyes onto CNTs. From the literature reviewed, it is observed that single walled carbon nanotubes (SWCNTs) show higher adsorption capacity than multi walled carbon nanotubes (MWCNTs) and functionalized and CNT composite have better sorption capacity than as grown CNTs. It is evident from the literature that CNT based nanosorbents have shown good potential for the removal of dyes from aqueous solution. However, still more research work should be focused on the development of cost effective, higher efficient and environmental friendly CNT based nanosorbents for their commercial applications.

Low-Cost Adsorbents: Growing Approach to Wastewater Treatment—a Review

Industrial, agricultural, and domestic activities of humans have affected the environmental system, resulting in drastic problems such as global warming and the generation of wastewater containing high levels of pollutants. As water of good quality is a precious commodity and available in limited amounts, it has become highly imperative to treat wastewater for removal of pollutants. In addition, the rapid modernization of society has also led to the generation of huge amount of materials of little value that have no fruitful use. Such materials are generally considered as waste, and their disposal is a problem. Also, there are some materials that are available in nature that have little or no use. The utilization of all such materials as low-cost adsorbents for the treatment of wastewater may make them of some value. An effort has been made to give a brief idea of an approach to wastewater treatment, particularly discussing and highlighting in brief the low-cost alternative adsorbents with a view to utilizing these waste/low-cost materials.

PHOTO-CATALYZED DEGRADATION OF HAZARDOUS DYE METHYL ORANGE BY USE OF A COMPOSITE CATALYST CONSISTING OF MULTI-WALLED CARBON NANOTUBES AND TITANIUM DIOXIDE

The high rate of electron/hole pair recombination reduces the quantum yield of the processes with TiO(2) and represents its major drawback. Adding a co-adsorbent increases the photocatalytic efficiency of TiO(2). In order to hybridize the photocatalytic activity of TiO(2) with the adsorptivity of carbon nanotube, a composite of multi-walled carbon nanotubes and titanium dioxide (MWCNT/TiO(2)) has been synthesized. The composite was characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared absorption spectroscopy (FTIR), and diffuse reflectance UV-vis spectroscopy. The catalytic activity of this composite material was investigated by application of the composite for the degradation of methyl orange. It was observed that the composite exhibits enhanced photocatalytic activity compared with TiO(2). The enhancement in photocatalytic performance of the MWCNT/TiO(2) composite is explained in terms of recombination of photogenerated electron-hole pairs. In addition, MWCNT acts as a dispersing agent preventing TiO(2) from agglomerating activity during the catalytic process, providing a high catalytically active surface area. This work adds to the global discussion of how CNTs can enhance the efficiency of catalysts.

Process development for the removal of lead and chromium from aqueous solutions using red mud--an aluminium industry waste.

Red mud, an aluminium industry waste, has been converted into an inexpensive and efficient adsorbent and used for the removal of lead and chromium from aqueous solutions. Effect of various factors on the removal of these metal ions from water (e.g. pH, adsorbent dose, adsorbate concentration, temperature, particle size, etc.) has been studied and discussed. The effect of presence of other metal ions/surfactants on the removal of Pb2+ and Cr6+ has also been studied. The material exhibits good adsorption capacity and the data follow both Freundlich and Langmuir models. Thermodynamic parameters indicate the feasibility of the process. Kinetic studies have been performed to understand the mechanism of adsorption. Dynamic modelling of lead and chromium removal on red mud has been undertaken and found to follow first-order kinetics. The rate constant and mass transfer coefficient have also been evaluated under optimum conditions of removal in order to understand the mechanism. Column studies have been carried out to compare these with batch capacities. The recovery of Pb2+ and Cr6+ and chemical regeneration of the spent column have also been tried.

Removal and recovery of Chrysoidine Y from aqueous solutions by waste materials.

This article describes the use of bottom ash [a power plant waste] and de-oiled soya [an agricultural waste] as effective adsorbents for the removal of a hazardous azo dye [Chrysoidine Y] from its aqueous solutions. This paper presents an experimental study and discussion of the adsorption characteristics of this dye on the two adsorbents. The adsorbents have been characterized, and also the effects of time, temperature, concentration, pH, and sieve size on the extent of adsorption have been evaluated. Batch adsorption measurements, kinetic studies, and column operations have been performed to elucidate the dye uptake capacity of the adsorbents. The monolayer adsorption capacities at 30 degrees C have been found from Langmuir analysis to be 7.27x10(-5) mol g(-1) and 3.35x10(-5) mol g(-1) for bottom ash and de-oiled soya, respectively. Adsorption kinetics experimental data are indicative of pseudo-second order kinetics during these processes. Column experiments indicate practical utility of the adsorbents for eradicating hazardous dyes from effluents. The recovery of the adsorbed dye from bottom ash and de-oiled soya, have been found to be 85% and 99%, respectively.

Multi-walled carbon nanotubes-ionic liquid-carbon paste electrode as a super selectivity sensor: Application to potentiometric monitoring of mercury ion(II)

In this article a super selectivity potentiometric methodology, using an ion-selective electrode, for determination of mercury ion(II) in aqueous solution was investigated. For modification of the electrode a room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIM·BF(4)), was applied as a super conductive binder, and Multi-walled carbon nanotubes (MWCNTs) was used in the composition of the carbon paste to improve conductivity and transduction of chemical signal to electrical signal. Moreover, incorporation of 1-(2-ethoxyphenyl)-3-(3-nitrophenyl)triazene (ENTZ) as an ionophore to this composition caused to significantly enhanced selectivity toward Hg(II) ions over a wide concentration range of 1.0×10(-4) to 5.0×10(-9) M with a lower detection limit of 2.5×10(-9) M (0.5 ppb) and a Nernstian slope of 29.3±(0.2) mV decade(-1) of Hg(II) activity. The electrode has a short response time (∼5s) and can be used for at least 55 days without any considerable divergence in potentials, and the working pH range was 2.0-4.3. Finally, the proposed electrode was successfully used as an indicator for potentiometric determination of Hg(II) in dental amalgam and water samples.

Column with CNT/magnesium oxide composite for lead(II) removal from water

BackgroundIn this study, manganese dioxide-coated multiwall carbon nanotube (MnO2/CNT) nanocomposite has been successfully synthesized.MethodsThe as-produced nanocomposite was characterized by different characteristic tools, such as X-ray diffraction, SEM, and FTIR. The MnO2/CNT nanocomposite was utilized as a fixed bed in a column system for removal of lead(II) from water. The experimental conditions were investigated and optimized. The pH range between 3 and 7 was studied; the optimum removal was found when the pH was equal to 6 and 7. The thickness of MnO2/CNT nanocomposite compact layer was also changed to find the optimum parameter for higher removal.ResultIt was observed that the slower the flow rates of the feed solution the higher the removal because of larger contact time.

Chromium removal by combining the magnetic properties of iron oxide with adsorption properties of carbon nanotubes.

The adsorption features of multiwall carbon nanotubes (MWCNTs) with the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. Composites of MWCNT/nano-iron oxide were prepared, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR). XRD suggests that the magnetic phase formed is maghemite and/or magnetite. FESEM image shows nano-iron oxides attached to a network of MWCNTs. The adsorption capability of the composites was tested in batch and fixed bed modes. The composites have demonstrated a superior adsorption capability to that of activated carbon. The results also show that the adsorptions of Cr(III) on the composites is strongly dependent on contact time, agitation speed and pH, in the batch mode; and on flow rate and the bed thickness in the fixed bed mode. Along with the high surface area of the MWCNTs, the advantage of the magnetic composite is that it can be used as adsorbent for contaminants in water and can be subsequently controlled and removed from the medium by a simple magnetic process.