Research Area


Physical Chemistry

(Surface Chemistry- Adsorption & Carbon Science, Environmental Chemistry, Groundwater Chemistry & Analytical Chemistry)

Use of an adsorption model John – Sivanandan Achari Isotherm Equation and Isotherm Plots as a method for the determination of adsorption capacity and surface area of porous materials from equilibrium isotherm Analysis John isotherm model log log P = C + n log V has many advantages in adsorption studies. The isotherm model is plotted between log log (p/p0×10N) against log V conform to a straight line in the case of most of the microporous materials. From this, limiting micropore volume (LMV) can be determined. The extended form John-Sivanandan Achari (J-SA) isotherm equation log log Ce = C + n log qe is most suitable (P.T. John and V. S. Achari, J. Mat. Sci. 2002, 37(4), 885-893; V. S Achari, Proc. Int. Conf. Carbon 2006, 3P107; T. Mercy and V. S. Achari, Proc. Int. Conf. MatCon 2016, 378- 382) for defining solid-liquid equilibria. The advantages of using these isotherm models include their usage commonly applicable for Type I, II and IV materials as per IUPAC classification. Conventional methods such as Dubinin - Radushkevich isotherm model or Langmuir isotherm model are usually applied only for Type I microporous adsorbents. Brunauer-Emmett-Teller (BET) isotherm model is usually applied in the relative pressure range 0.05-0.3 only as regards to most of the adsorption systems in solid-gas equilibria. John isotherm models are distinct for their usages with sharp kinks or phases appear at points of monolayer completion, mesopore filling, capillary condensation and saturation for materials having micro, meso and macropores. Therefore, John isotherm method is called phase change method. In this research work, the evaluation of the isotherm plots, their unique features and constants of John isotherm models are done on microporous, mesoporous and nanoporous materials based on the data published on adsorption systems. This is performed on the basis of different perspectives with respect to the nature of materials reported by the researchers and suitability of the data for the above isotherm models. The researchers in these selected reported works mostly used activated carbons in their physical, chemical or thermally surface treated modified forms. Based on some of the selected data, John isotherm studies are performed and the results are presented in this thesis along with a series of new materials developed. The John isotherm studies on adsorbents such as carbon nanotubes, polymer supported, biological and some representative adsorbents other than carbon also constitute new areas of research initiatives. These isotherm models are also applied on some newly developed nano metal ion (M3+) incorporated granular activated carbons. This research study comprises evaluation of adsorption isotherm parameters of John and John-Sivanandan Achari isotherm models and their structural constants. The comparison of constants are done with different isotherm models Langmuir (L), Freundlich (Fr), modified Freundlich (F), Dubinin-Radushkevich (D-R), Brunauer-Emmett-Teller (BET) and I plots for microporous, mesoporous, nanoporous carbon nanotubes (SWCNT/MWCNT) and surface treated carbons based on pore volumes and surface area for both solid–gas and solid-liquid equilibria. Outcome of this research will be useful for the study of porous materials for their structural characterisation for those in the field of adsorption science and engineering.John isotherm model [log logP =C + n logV] is found most successful for determining adsorption efficiency, porosity and surface area of micro porous materials. The precise information about the phase changes during adsorption process are revealed, in the entire range of relative pressure, from the very low pressure region up to the saturation level in a single and direct empirical plot is one of the greatest advantages. Each adsorption phase is characterised by adsorbability constants ‘n’ and adsorbed quantity ‘V’. The results of regression analysis of John (J) isotherm model in comparison with other two parameter isotherm models indicate closer fit of the data in the case of most of the porous materials. A comparison of adsorption capacity V(J)and surface area SA(J) determined in comparison with other isotherm models are in excellent agreement. The separation of adsorption and pore filling phenomena as visible through different phases in the solid-liquid adsorption in John –Sivanandan Achari (J-SA) isotherm [log log Ce = C + n log qe] are very much helpful to recognize and thereby interpret both specific and non-specific interactions occur during the adsorption process. Many a micro porous carbons have molecular sieve effects or activated diffusion effect during pore filling phenomena at low pressure ranges. The regions of adsorptions as regards to pore dimensions of finer pores, coarser pores and their saturation at p/p~ 1.0 is becoming visible in both (J) isotherm for solid-gas equilibrium and (J-SA) isotherm for solid-liquid equilibrium. John–Sivanandan Achari (J-SA) isotherm model describes the adsorption process effectively for wide ranges of low concentrations, is of greatest advantage to apply in adsorption systems with very low contaminant level in water pollution studies testing and monitoring. John isotherms, of mesoporous carbon materials, are compared and found excellent agreement of results with earlier published. Isotherms are characterised by definite slope taken as the measure of adsorption intensity (n). The distinct phase changes give information for the categorisation of the micro and mesopores. John isotherm plot of a-MCMBs distinctively provide well defined phases of adsorption to interconnect the entire porous structure, offer the possibility for exposing the micropore and mesopore surface area from a single graph, through an isotherm subtraction method. The D-R plots show the respective Type a, b and c variation for mesoporous carbons graphene, a-MCMBs and ordered mesoporous carbons respectively. I- plot of graphene devoid of any sharp mesoporous I-point, indicates the presence of microporosity in it, accounted from the first sharp kink of John isotherm model. The provision for the exact determination of relative pressure p/p0 (eg. MPSC, MPSC-MC, MPSC-FB and MPSC-BY are mentioned) for the pore filling phenomena monolayer completion, multilayer formation and capillary condensation, distinctly visible through the sharp kinks in John isotherm model is of great advantage. John–Sivanandan Achari (J-SA) isotherm plots for MPC, MPSC and MPSC/C carbon for MC adsorption, DBT adsorption on template derived mesoporous carbons and Direct Yellow dye adsorption on CMK-3 and PAC also show distinct adsorption phases for the Type I isotherm. Their adsorption efficiency are critically enumerated. In this chapter, John isotherm studies of carbon nanotubes are discussed in detail. Adsorption systems taken up for the study include both single walled and multiwalled carbon nanotubes (SWCNTs and MWCNTs) and their surface treated and chemically modified forms. The John isotherm of raw and O2 plasma oxidised MWCNTs for their N2 isotherm study is followed by the study of John-Sivanandan Achari (J-SA) isotherm study of adsorption of removal of Pb2+ ions at different temperatures. The J-SA isotherm studies on oxidised MWCNTs for the Ni(II) adsorption is studied. John isotherm studies for the nitrogen adsorption at 77K on polymeric materials such as PPO, poly(2,6-dimethyl -1,4-phenylene oxide) activated and nonactivated carbon are studied. Further John isotherm studies on melamine formaldehyde resins are conducted. Biological adsorption systems are studied for their J-SA isotherms. Adsorption of myoglobin on biomimetic hydroxyl apatite nanocrystals; adsorption of doxorubicin on Ap-SWNTs, adsorption of a model protein bovine serum albumin (BSA) on SWNT, cytochrome adsorption on CMK-3-130 are analysed for their (J-SA) isotherm features. Adsorption of ethyl acetate (EA) on chromium terephthalate based crystals is representatively done for John isotherm study. The J-SA isotherm adsorption capacities for uranyl adsorption on PAN template zirconium titanate and adsorption of Co(II) and Mn(II) on 001×7×7 ion-exchange resin are determined representatively for porous adsorbents other than carbon. The adsorption efficiencies Vm(J) for solid-gas equilibria or qm(J-SA) for solid-liquid equilibria are determined and are shown in respective tables and figures for comparison with the reported adsorption capacities or pore volumes. John (J) isotherm plots are drawn for the series of newly developed carbons, the base carbon being GAC 383 and the metal ion incorporated carbons GAC CN383, GAC CN473, GAC CN673, GAC CN873, GAC CN1073 and GAC CN1273. The isotherm behaviour is well explained over distinct phases. The John-Sivanandan Achari isotherm plots are created for the adsorption of Methylene blue, Phenol and p-Nitrophenol (PNP) and the different pore filling mechanisms are explained over distinct phases. The pore volumes obtained using John isotherm Vm(J) is compared to micropore volume of D-R Vm(D-R), BET monolayer capacity Vm(BET) and monolayer volume using I point Vm(I) and micropore volume using t plot Vmicro(t plot). Surface area obtained using Vm(J) is SA1(J) and compared to SA(D-R), SA(BET), SA(I) and SAmic (t plot). The adsorption efficiencies obtained using John –Sivanandan Achari isotherms are compared to Langmuir, Dubinin-Radushkevich and Freundlich for J-SA isotherm studies for testing the validity of these isotherm models. The activation improved the relative proportion of microporosity as evidenced by the Vm(J) values and adsorbability constant (n). GAC 1273 has uniform micropores with a single phase in John isotherm having LMV (Limiting Micropore Volume) of 406 cm3/g. The gas-solid equilibria have mostly two phases marked by the Type I isotherm with both finer and coarser pores. Study concludes with the following remarks that John isotherm models are useful for the structural characterisation of most of the porous materials studied. Variability among the indices evaluated is within the permitted limit on comparison with other isotherm models. Testing and evaluation is done for more than one hundred and thirty three (133) adsorption systems in (solid-gas) and (solid-liquid) equilibria consisting of microporous, mesoporous, carbon nanotubes, granular activated carbons and other porous materials following Type I, II and IV feature as per IUPAC 2015 classification of physisorption systems. John (J) isotherm and its extended form John-Sivanandan Achari (J-SA) isotherms can be used for the study of adsorption features, porosity, pore volume, adsorption capacity, adsorbability constant and surface area of adsorbents, activated carbons, powders, carbon nanotubes and similar porous materials.

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