Publications by authors named "Sankar Chakma"

12 Publications

  • Page 1 of 1

Kinetics, degradation mechanisms and antibiotic activity reduction of chloramphenicol in aqueous solution by UV/HO process.

Water Sci Technol 2021 Aug;84(3):524-537

Department of Chemical Engineering, Indian Institute of Science Education and Research Bhopal, Bhopal 462066, India.

In this study, the aim was to explore the effectiveness of the UV/HO photolysis (UVP) process in terms of antimicrobial activity reduction and increasing the mean oxidation number of carbon (MONC) under the degradation of chloramphenicol (CHPL) drug. CHPL degradation kinetics and the effects of foreign anions on CHPL degradation were explored in this study. The order of the inhibition effect was found as Cl > NO > HCO due to their different in HO radical scavenging capacity. A pseudo-first-order model for CHPL degradation was well established, and the rate constant (k) was 2.93 × 10 min (R = 0.98) in UVP. Thirteen intermediate products were detected in MS-chromatogram and were identified through different proposed degradation pathways. The cleavage of the amide side chain in CHPL was more effective in CHPL degradation due to an electrophilic attacks by HO radicals on it. The inactivation rates of E. coli were decreased due to the reduction of -NO group into -NH functional group in CHPL that leads to the production of low toxic compounds on CHPL degradation.
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http://dx.doi.org/10.2166/wst.2021.254DOI Listing
August 2021

Experimental and theoretical study of deep oxidative desulfurization of Dibenzothiophene using Oxalate-Based catalyst.

Ultrason Sonochem 2021 Jul 29;75:105580. Epub 2021 Apr 29.

Department of Chemical Engineering, Indian Institute of Science Education and Research Bhopal, Bhopal 462066, Madhya Pradesh, India. Electronic address:

The present study reports the experimental and theoretical investigation for production of ultra-low sulfur liquid fuels through estimation of various reactive species formed during the reaction with the help of simulation. All the experiments were performed using an ultrasound bath which operates at a frequency of 37 kHz and a theoretical power of 95 W. The presented oxalate-based technique is found to be more efficient with > 93% DBT oxidation within 15 min of reaction time at 25 °C due to formation of reactive species like FeCO and [Formula: see text] which accelerate the reaction kinetics. Moreover, we have also investigated the influence of process parameters such as molar ratio of CO/Fe, oxidant concentration, volume ratio of organic to aqueous phase, sulfur concentration, and activation methods of oxidant. The results revealed that catalyst can be reused for several runs without decrease in catalytic activity. The experimental and simulation of cavitation bubble dynamics results revealed that sonochemical effect assists to accelerate the reaction kinetics through formation of free radicals (O, H, OH and HO) and other reactive species like O and HO generated during transient cavitation. The sono-physical effects of cavitation help to create a fine emulsion in the liquid-liquid heterogeneous system leading to enhanced mass transfer rate by providing more interfacial surface area for occurring chemical reaction.
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http://dx.doi.org/10.1016/j.ultsonch.2021.105580DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8135043PMC
July 2021

A critical analysis of sono-hybrid advanced oxidation process of ferrioxalate system for degradation of recalcitrant pollutants.

Chemosphere 2021 Aug 19;277:130324. Epub 2021 Mar 19.

Department of Chemical Engineering, Indian Institute of Science Education and Research Bhopal, Bhopal, 462 066, Madhya Pradesh, India. Electronic address:

The emerging contaminants in wastewater discharged from numerous chemical process industries, pharmaceutical industries, textile, and wineries have attracted the attention of the scientific community due to their toxicity and persistence in the environment. The conventional techniques are incompetent to treat many of such recalcitrant toxic pollutants. To achieve high mineralization, advanced oxidation processes (AOPs) are found to be more efficient for the degradation of these organic pollutants without producing secondary pollutants with no/less amount of sludge. The primary oxidation agents for AOPs are in-situ generated free radicals, which are highly reactive and effective oxidants for degrading any type of organic molecules present in the wastewater. In the past decades, the combination of AOPs or simultaneous application of more than one AOP has been investigated extensively for wastewater treatment and these hybrid-AOPs have been reported to be beneficial for high-level mineralization of organic pollutants. This paper presented the characteristics, properties and influence of parameters in sono-photo-ferrioxalate system. The primary operating parameters in sono-photo-ferrioxalate system that affect the kinetics are defined as the solution pH, temperature, molar ratio of Fe/CO, HO concentration, source of light, ultrasound intensity, dissolved gases, and size of cavitation bubble. In this process, several oxidizing radicals are generated such as HO, HO, CO, CO and O which are also responsible for degradation. In this review, we have mainly addressed the degradation of recalcitrant pollutants using the sono-photo-ferrioxalate system and a critical analysis of process parameters that influence mineralization efficiency.
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http://dx.doi.org/10.1016/j.chemosphere.2021.130324DOI Listing
August 2021

Sonochemical synthesis of amphoteric Cu-Nanoparticles using Hibiscus rosa-sinensis extract and their applications for degradation of 5-fluorouracil and lovastatin drugs.

J Hazard Mater 2020 11 28;399:123035. Epub 2020 May 28.

Department of Chemical Engineering, Indian Institute of Science Education and Research, Bhopal, 462 066 Madhya Pradesh, India. Electronic address:

Recent studies reported the detection of numerous emerging and active pharmaceutical constituents in the ground and surface water. To address these issues, the present study reported the ultrasound-assisted synthesis of zero-valent copper (Cu) nanoparticles using Hibiscus rosa-sinensis extract as reducing and stabilizing agent. The catalyst was characterized using XRD, SEM, EDX, PSA, BET, etc., and the results revealed that sonochemical synthesis technique influenced the crystallinity with controlled growth of Cu. While the hard ligand hydroxyl group (-OH) reduces the Cu to Cu and soft ligand carbonyl group (CO) present in the oxidized polyphenols helps in capping and stabilizing the Cu-nanoparticles. During the ultrasound application, continuous release of Cu from Cu promoted the degradation by producing OH and O radicals. Approx. 91.3 % and 93.2 % degradation efficiencies were achieved for 5-fluorouracil and lovastatin. The results showed that Cu nanoparticles were amphoteric in nature and the synergy calculation revealed that ultrasound has a direct influence on degradation of drugs which are difficult to degrade/mineralize using conventional techniques. Based on the results, a possible degradation mechanism of drug molecules in the presence of oxidants, zero-valent copper and ultrasound has been proposed.
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http://dx.doi.org/10.1016/j.jhazmat.2020.123035DOI Listing
November 2020

Mechanistic investigation in degradation mechanism of 5-Fluorouracil using graphitic carbon nitride.

Ultrason Sonochem 2019 Jan 24;50:311-321. Epub 2018 Sep 24.

Department of Chemical Engineering, Indian Institute of Science Education and Research, Bhopal 462066, M.P., India. Electronic address:

The present study reports the synthesis of metal-free polymeric catalyst, graphitic carbon nitride (g-CN), through sonochemical method followed by thermal treatment. The synthesized g-CN was characterized using XRD, DRS, FESEM, TGA, EDX, etc. and the characterization results revealed that it possesses medium band-gap energy, high thermal and chemical stability. The photo-activity of the catalyst was also evaluated using degradation of 5-Fluorouracil under different experimental conditions. The results revealed that the addition of HO during sonolysis process did not show any significant synergy. This is attributed to the low vapor pressure of HO that does not allow it to diffuse into the cavitation bubble to produce OH radicals through sonolysis process. Using sono-hybrid process, more than 90% degradation was seen within 5 min of treatment with a rate constant of 3.95 × 10 s. In alkaline medium, 5-Fluorouracil degradation occurred through defluorination and subsequently substitution of -OH group to the aromatic ring leading to formation of intermediates such as 2-fluoro-3-oxopropanoic acid and urea. While sono-hybrid advanced oxidation processes (AOPs) helped towards complete mineralization through formation of smaller molecular compounds such as maleic acids, lactic acids, propanol, etc. On the other hand, the maximum synergy effect of ∼2.4 was seen for sonocatalysis process followed by hybrid-AOPs of (US + g-CN + HO + UVC) with a synergy factor of ∼2.2. Also, the synthesized catalyst exhibited the same catalytic activity even after 5 runs of sono-photocatalysis process for degradation of 5-Fluorouracil.
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http://dx.doi.org/10.1016/j.ultsonch.2018.09.032DOI Listing
January 2019

Ionic Liquid Facilitated Dehydrogenation of -Butylamine Borane.

ACS Omega 2018 Feb 26;3(2):2273-2281. Epub 2018 Feb 26.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India.

The current work reports ionic liquid (IL) facilitated dehydrogenation of -butylamine borane (TBAB) at 90 and 105 °C. For the screening of potential IL solvent, solubility predictions of TBAB in ILs were performed by the conductor-like screening model segment activity coefficient (COSMO-SAC) model. The COSMO-SAC model predicted a logarithmic infinite dilution activity coefficient of -6.66 and -7.31 for TBAB in 1-butyl-3-methylimidazolium acetate [BMIM][OAc] and trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate [TDTHP][Phosph], respectively. Hydrogen (1.95 equiv) was seen to release from TBAB/[BMIM][OAc] at 105 °C, whereas TBAB/[TDTHP][Phosph] produced 1.63 equiv of hydrogen after 360 min of dehydrogenation. The proton nuclear magnetic resonance (H NMR) characterization of TBAB/IL systems revealed the structural integrity of ILs during dehydrogenation. Further characterization through the boron NMR (B NMR) technique disclosed the time-resolved formation and stability of the starting compound, intermediate boron moieties, and product distribution. The B NMR characterization also revealed the fact that the TBAB/[TDTHP][Phosph] mixture dehydrogenates via bimolecular addition of TBAB by forming borohydride anion (-BH ). It was seen to oligomerize with the subsequent addition of TBAB in the oligomer chain. For the TBAB/[BMIM][OAc] system, the B NMR characterization could not identify the borohydride anion but confirmed a faster formation of the B=N moiety when compared to the TBAB/[TDTHP][Phosph] system. On the basis of the NMR characterization, IL-facilitated dehydrogenation mechanism of TBAB is proposed.
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http://dx.doi.org/10.1021/acsomega.7b01781DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6641282PMC
February 2018

Mechanistic investigations in sono-hybrid (ultrasound/Fe/UVC) techniques of persulfate activation for degradation of Azorubine.

Ultrason Sonochem 2017 Sep 11;38:652-663. Epub 2016 Aug 11.

Department of Chemical Engineering, Indian Institute of Technology, Guwahati 781 039, Assam, India. Electronic address:

Persulfate-based oxidation of recalcitrant pollutants has been investigated as an alternative to OH radical based advanced oxidation processes due to distinct merits such as greater stability and non-selective persistent reactivity of SO oxidant species. The present study has attempted to highlight mechanistic features of persulfate-based decolorization of textile dye (Azorubine) using sono-hybrid techniques of activation. Three activation techniques, viz. sonolysis, Fe ions and UVC light and combinations thereof, have been examined. UVC is revealed to be the most efficient decolorization technique. The mechanism of sonolysis (i.e. thermal activation of persulfate in the bubble-bulk interfacial region) is revealed to be almost independent of the mechanism of UVC. Fe activation is revealed to have an adverse interaction with UVC due to scavenging of sulfate radicals by Fe ions. The best hybrid activation technique for persulfate-based degradation and mineralization of Azorubine is UVC+ultrasound. Due to independent mechanisms, degradation and mineralization of the dye obtained with simultaneous application of UVC and ultrasound is nearly equal to the sum of degradation and mineralization obtained using individual techniques.
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http://dx.doi.org/10.1016/j.ultsonch.2016.08.015DOI Listing
September 2017

Investigations in sono-enzymatic degradation of ibuprofen.

Ultrason Sonochem 2016 Mar 2;29:485-94. Epub 2015 Nov 2.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India. Electronic address:

The drug ibuprofen (IBP) appears frequently in the wastewater discharge from pharmaceutical industries. This paper reports studies in degradation of IBP employing hybrid technique of sono-enzymatic treatment. This paper also establishes synergy between individual mechanisms of enzyme and sonolysis for IBP degradation by identification of degradation intermediates, and Arrhenius & thermodynamic analysis of the experimental data. Positive synergy between sonolysis and enzyme treatment is attributed to formation of hydrophilic intermediates during degradation. These intermediates form due to hydroxylation and oxidation reactions induced by radicals formed during transient cavitation. Activation energy and enthalpy change in sono-enzymatic treatment are lower as compared to enzyme treatment, while frequency factor and entropy change are higher as compared to sonolysis. Degradation of IBP in sono-enzymatic treatment is revealed to be comparable with other hybrid techniques like photo-Fenton, sono-photocatalysis, and sono-Fenton.
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http://dx.doi.org/10.1016/j.ultsonch.2015.11.002DOI Listing
March 2016

Investigations in physical mechanism of the oxidative desulfurization process assisted simultaneously by phase transfer agent and ultrasound.

Ultrason Sonochem 2015 May 13;24:98-106. Epub 2014 Nov 13.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India. Electronic address:

This paper attempts to discern the physical mechanism of the oxidative desulfurization process simultaneously assisted by ultrasound and phase transfer agent (PTA). With different experimental protocols, an attempt is made to deduce individual beneficial effects of PTA and ultrasound on the oxidative desulfurization system, and also the synergy between the effects of PTA and ultrasound. Effect of PTA is more marked for mechanically stirred system due to mass transfer limitations, while intense emulsification due to ultrasound helps overcome the mass transfer limitations and reduces the extent of enhancement of oxidation by PTA. Despite application of PTA and ultrasound, the intrinsic factors and properties of the reactants such as polarity (and hence partition coefficient) and diffusivity have a crucial effect on the extent of oxidation. The intrinsic reactivity of the oxidant also plays a vital role, as seen from the extent of oxidation achieved with performic acid and peracetic acid. The interfacial transport of oxidant in the form of oxidant-PTA complex reduces the undesired consumption of oxidant by the reducing species formed during transient cavitation in organic medium, which helps effective utilization of oxidant towards desulfurization.
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http://dx.doi.org/10.1016/j.ultsonch.2014.11.008DOI Listing
May 2015

Investigation in mechanistic issues of sonocatalysis and sonophotocatalysis using pure and doped photocatalysts.

Ultrason Sonochem 2015 Jan 18;22:287-99. Epub 2014 Jun 18.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India. Electronic address:

This paper attempts to investigate the mechanistic issues of two hybrid advanced oxidation processes (HAOPs), viz. sonocatalysis and sonophotocatalysis, in which the two individual AOPs, viz. sonolysis and photocatalysis, are combined. Three photocatalysts, viz. pure ZnO and Fe-doped ZnO (with two protocols) have been employed. Fe-doped ZnO catalyst has been characterized using standard techniques. Decolorization of two textile dyes has been used as the model reaction. With experiments that alter the characteristics of ultrasound and cavitation phenomena in the medium, the exact synergy between the two AOPs has been determined using a quantitative yard stick. The results revealed a negative synergy between the two AOPs, which is an almost consistent result for decolorization of both dyes using all three photocatalysts. Fe-doping of ZnO catalyst helps in generation of more OH radicals that could augment decolorization. However, these radical mainly react with dye molecules adsorbed on catalyst surface. Intense shock waves generated by cavitation bubbles cause desorption of dye molecules from catalyst surface and reduce the probability of dye-radical interaction, thus reducing the net utility of photochemically generated OH radicals towards dye decolorization. This is rationale underlying the negative synergy between sonolysis and photocatalysis. Fe-doped ZnO catalyst increases the extent of decolorization, but the synergy between the two individual AOPs remains unaltered with doping.
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http://dx.doi.org/10.1016/j.ultsonch.2014.06.008DOI Listing
January 2015

Mechanistic insight into sono-enzymatic degradation of organic pollutants with kinetic and thermodynamic analysis.

Ultrason Sonochem 2014 Jul 10;21(4):1400-6. Epub 2014 Feb 10.

Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India; Center for Energy, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India. Electronic address:

In this paper, we have attempted to get a physical insight into process of sono-enzymatic treatment for degradation of recalcitrant organic pollutants. Decolourization of an azo dye has been used as model reaction with different experimental protocols that alter characteristics of ultrasound and cavitation phenomena in the system. Experimental data is analyzed to determine kinetic and thermodynamic parameters of decolorization process. The trends observed in kinetic and thermodynamic parameters of decolourization are essentially manifestations of the dominating mechanism of the decolorization of the textile dye (or nature of prevalent chemical reaction in the system), viz. either molecular reaction due to enzyme or radical reaction due to transient cavitation. The activation energy for sonochemical protocol is negative, which indicates instantaneity of the radical reactions. The frequency factor is also low, which is attributed to high instability of radicals. For enzymatic and sono-enzymatic protocols, activation energy is positive with higher frequency factor. Enthalpy change for sonochemical protocol is negative, while that for enzymatic and sono-enzymatic protocols is positive. The net entropy change for sonochemical protocol is more negative than enzymatic or sono-enzymatic protocol due to differences in prevalent chemical mechanism of dye decolorization. Due to inverse variations of frequency factor and activation energy, marginal rise in reaction kinetics is seen for sono-enzymatic protocol, as compared to enzymatic treatment alone. Due to inverse variations of enthalpy and entropy change, net Gibbs energy change in all experimental protocols shows little variation indicating synergism of the mechanism of ultrasound and enzyme.
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http://dx.doi.org/10.1016/j.ultsonch.2014.01.028DOI Listing
July 2014

Mechanistic insight into sonochemical biodiesel synthesis using heterogeneous base catalyst.

Ultrason Sonochem 2014 Jan 16;21(1):169-81. Epub 2013 May 16.

Center for Energy, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India.

The beneficial effect of ultrasound on transesterification reaction is well known. Heterogeneous (or solid) catalysts for biodiesel synthesis have merit that they do not contaminate the byproduct of glycerol. In this paper, we have attempted to identify the mechanistic features of ultrasound-enhanced biodiesel synthesis with the base-catalyst of CaO. A statistical design of experiments (Box-Behnken) was used to identify the influence of temperature, alcohol to oil molar ratio and catalyst loading on transesterification yield. The optimum values of these parameters for the highest yield were identified through Response Surface Method (with a quadratic model) and ANOVA. These values are: temperature=62 °C, molar ratio=10:1 and catalyst loading=6 wt.%. The activation energy was determined as 82.3 kJ/mol, which is higher than that for homogeneous catalyzed system (for both acidic and basic catalyst). The experimental results have been analyzed vis-à-vis simulations of cavitation bubble dynamics. Due to 3-phase heterogeneity of the system, the yield was dominated by intrinsic kinetics, and the optimum temperature for the highest yield was close to boiling point of methanol. At this temperature, the influence of cavitation bubbles (in terms of both sonochemical and sonophysical effect) is negligible, and ultrasonic micro-streaming provided necessary convection in the system. The influence of all parameters on the reaction system was found to be strongly inter-dependent.
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http://dx.doi.org/10.1016/j.ultsonch.2013.04.010DOI Listing
January 2014
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