Study Of Novel Bentonite Based Composites For The Alleviation Of Heavy Metals And Dyes Contamination Via Adsorption And Degradation

Thriving urbanization and resultant elevation in industrialization caused an uncompensated rise in water pollution via uncontrolled dumping of heavy metals and dye wastes.This contamination has severely affected the ecosystem due to the non-biodegradable and bio accumulative nature of most of the water contaminants specifically heavy metals.These heavy metals and organic dyes are termed as notorious entities owing to their potential to cause carcinogenic,mutagenic and various other lethal health effects both in animals and humans.It is the imperative need of time to combat this contamination as water is the basic element of life and is used from drinking to household tasks to large scale industrial use.Among various adopted method to combat this problem,adsorption and degradation removal pathway of contaminants are deemed to be ideal due to their handy operation and the enchanting outcomes.For that,enormous adsorbents have so far been reported in the literature and the clay materials are among the most efficient ones which include bentonites.Many studies have documented the use of bentonite for the mitigation of water pollutants,yet the suppressed activity and tedious adsorbent separation make its applicability unwanted in certain circumstances.Therefore,the work planned for this Ph.D.thesis was to modify the bentonite and engineer its composites which would possess enhanced pollutants adsorbing activity accompanying the ease of adsorbent/composite material separation after the required application has been achieved and for that three novel bentonite composite materials were fabricated and the results are described as（1）This study reports a facile fabrication route for hydroxyapatite（HAp）nanoparticles impregnated magnetic bentonite（HAp@Fe₃O₄@bentonite）composite,which was in turn applied for the removal of(Pb（II）,(Cd（II）and crystal violet（CV）dye from aqueous solution.Adsorption isotherm data best fitted with Freundlich isotherm model and kinetic behavior adopted pseudo-second order adsorption mechanism attaining equilibrium in 60 min over a wide p H range（2.0-13）.HAp@Fe₃O₄@bentonite realized higher adsorption capacity for Pb（II）,Cd（II）and CV（404.56,310.36 and 1201.30 mg/g respectively）than the acid-treated bentonite（161.28,155.7 and 740.14 mg/g）and was magnetically separable.Similarly,the higher Langmuir maximum adsorption capacity exhibited by HAp@Fe₃O₄@bentonite for Pb（II）,Cd（II）and CV（482,309 and1290 mg/g respectively）was attributed to the surface functionalities(-OH,-NH₂,-PO₄^3-).Fresh and spent adsorbents were characterized by FTIR,XRD,DTG,BET surface area analysis,SEM,EDX,and VSM techniques.HAp@Fe₃O₄@bentonite composite exhibited BET surface area of 73.72 m2/g,pore volume of 0.026 cm3/g and an average particle size of 81.39 nm.The composite remained active for five successive adsorption reuses with minimal loss in adsorption capacity as confirmed by FTIR and XRD analyses.The newly synthesized HAp@Fe₃O₄@bentonite composite possessing high adsorption efficiency for Pb（II）,Cd（II）and CV,can be envisaged as a promising solution for wastewater treatment.（2）Decontamination of dye loaded water has become an issue of intensive interest on both,basic research and industrial scale.Herein,I report the fabrication of bentonite/APTMA（3-（acrylamidopropyl）trimethylammonium chloride）and Fe₃O₄-bentonite/APTMA adsorbents via a facile synthesis route and commonly available raw materials.The structural and morphological characteristics of the synthesized adsorbents were studied by BET,XRD,FTIR,VSM,SEM,EDX and XPS techniques and were tested for their adsorption capacity for cationic crystal violet（CV）and anionic Congo red（CR）dyes.Fe₃O₄-bentonite/APTMA exhibited BET surface area and pore volume of 27.8 m²/g and0.012 cm3/g respectively and superior adsorption than bentonite/APTMA with maximum calculated adsorption capacity of 2286 and 1210 mg/g for CV and CR respectively.Behavior of both the adsorbents revealed the hydrophobic nature of bentonite/APTMA which could be attributed to its lower adsorption capacity as compared to super-hydrophilic Fe₃O₄-bentonite/APTMA.Effect of operating parameters like p H,adsorbent dosage,dye concentration and temperature were studied,and it was observed that the efficiency of adsorbents was further enhanced towards dye removal in the presence of heavy metal ions and in model wastewater which was attributed to the synergistic effect of metal ions during adsorption process.Adsorption process was endothermic with fast reaction kinetics suggesting the predominant occurrence of chemisorption.Adsorption mechanism was dominated by the occurrence of hydrogen bonding and the electrostatic interactions between adsorbent and dye molecules.This study can be of great industrial prospects for the remediation of CR and CV and other similar dyes and organic pollutants from wastewater both,in the presence as well as absence of heavy metals ions.（3）Owing to the increasing demand of environmentally benign materials for the degradation of hazardous dyes,herein we are reporting two different synthesis approaches for the fabrication of iron loaded bentonite composites by modifying and activating bentonite surface with polydopamine（PDA）followed by pillaring with Fe³⁺（Fe-PDA-bentonite）and Fe₃O₄（Fe₃O₄-PDA-bentonite）.Both the composites were assessed for their adsorption and degradation performance using crystal violet（CV）,Rhodamine B and Brilliant blue dyes by adopting advanced oxidation process type Fenton reaction under variable energy sources（Sunlight,UV light and Ultrasonication）,concentration of H₂O₂ and catalyst dosage.Under UV light irradiation,the composites achieved complete degradation of the dyes within 60 min and showed degradation rate constant of 30.5×10^-3 to 81.8×10^-3min^-1Textural characterizations of the composites were achieved via XRD,FTIR,TGA,XPS,SEM-EDX,TEM,N₂ adsorption,VSM and UV/Vis spectrophotometry.The adsorption data for CV over two composites fitted well with Langmuir adsorption isotherm,exhibiting the maximum adsorption capacities of 862 mg/g and 1235 mg/g for Fe-PDA-bentonite and Fe₃O₄-PDA-bentonite composites respectively.LCMS analysis of the post degradation products revealed that both the composites followed different degradation pathways and Fe₃O₄-PDA-bentonite showed superior photocatalytic performance by accomplishing complete dye degradation without leaving any degradation products.FTIR analysis of the post-degradation composites confirmed their structural stability with negligible iron leaching.This study,accredited to its cost-effectiveness,ease of operation and high efficiency,provides useful reference information for the degradation of dyes at industrial level.