Chromium vi removal from aqueous solution by using silver nano activated carbon

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY HA THI LAN ANH CHROMIUM (VI) REMOVAL FROM AQUEOUS SOLUTION BY USING SILVER NANO-ACTIVATED CARBON BACHELOR THESIS Study Mode: Full-time Major: Environmental Science and Management Faculty: Advanced Education Program Office Batch: 2014 - 2018 Thai Nguyen, 25/09/2018 Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor of Environmental Science and Management Student name Ha Thi Lan Anh Student ID DTN 1454290001 Thesis title Chromium (VI) removal from aqueous solution by using Silver nano-activated carbon Supervisor(s) Dr Van Huu Tap (Faculty of Environment and Earth Science, Thai Nguyen University of Sciences) Abstract: Chromium (Cr(VI)) is a heavy metal that can cause a serious impact on the environment and human – being The treatment of Cr(VI) was reported through several methods such as chemical precipitation, adsorption, membrane filtration, coagulation/flocculation, ion exchange and absorption However, absorption is considered one of the most idea method for Cr(VI) removal Activated carbon is a low-cost material derived from wood or other organic waste from the shell and coir As the main constituent of coal is carbon, so all the carbon-rich fuels can be used to make activated carbon Besides, silver nano particles as a catalyst for modifying activated carbon to increase the adsorption capacity of activated carbon In this study, the activated carbon loaded silver nanoparticle (AgNPs-AC) was used as a low-cost adsorbent to remove Cr (VI) from the aqueous solution Batch absorption i experiments were conducted to evaluate the effects of pH, initial concentrations of Cr(VI), contact time and dose of AgNPs-AC on Cr(VI) removal efficiency The results showed that at pH = 4, contact time of 180 min, 20mg AgNPs-AC/25mL of K2Cr2O7 solution with initial Cr(VI) concentration at mg/L were the most suitable conditions for adsorption of Cr VI) from aqueous solutions The optimum adsorption capacity achieved after processing was 27.70mg/g at 20 mg/25mL of AgNPs-AC dose and 40 mg/L initial Cr(VI) The adsorption kinetic data were found to fit well with the pseudo-first and second order models with very high correlation coefficients From this study, it can be concluded that AgNPs-AC is an interesting adsorbent, saving, easy to remove Cr (VI) from the aqueous solution Keywords Silver nano-activated carbon, Chromium, Adsorption capacity, Activated carbon Number of pages: 40 Date of submission: 25/09/2018 ii ACKNOWLEDGEMENT First of all, I would like to thank you teachers at University of Agriculture and Forestry – University of Thai Nguyen has dedicated teaching me during the period of study at the school I would like to express deep gratitude to the teachers Dr Van Huu Tap whose guidance, encouragement, suggestion and very constructive criticism have contributed immensely to the evolution of my ideas during the project Without his guidance, I may not have this report At the same time, I also want to express my deep gratitude to Dr Vu Xuan Hoa, who gave me a chance to interact with a nanotechnology field I also thank faculty of Environment and Earth Science – Thai Nguyen University of Sciences - Thai Nguyen University has facilitated me throughout the course of the thesis Finally yet important, I took this opportunity to express my deepest appreciation to my families, relatives, friends who encouraged and supported me unceasingly and all who directly or indirectly, have lent their helping hand in this venture Thank you all very much! Thai Nguyen, 25/09/2018 Student Ha Thi Lan Anh iii TABLE OF CONTENTS ACKNOWLEDGEMENT iii TABLE OF CONTENTS iv LIST OF FIGURES vi LIST OF TABLES vii PART I INTRODUCTION 1.1 Research rationale 1.2 Research's objectives: .2 1.3 Research hypotheses: 1.4 Limitations 1.5 Definitions………………………………………………………………………………………….3 PART II LITERATURE REVIEW 2.1 Chromium 2.1.1 Electronic and molecular structure of hexavalent chromium compounds .4 2.1.2 Sources of Chromium .5 2.2 Routes of exposure (Chromium) .5 2.2.1 Air 2.2.2 Drinking-water .6 2.2.3 Food 2.3 Coconut shell activated carbon 2.4 Silver nanoparticles 2.5 Silver nano-activated carbon (AgNPs-AC) .8 PART III METHOD .9 iv 3.1 Materials 3.1.1 Chemicals .9 3.1.2 Adsorbent materials 3.1.3 Laboratory instruments 10 3.2 Location and research time 11 3.3 Research Contents 11 3.4 Adsorption experiments of Chromium (Cr6+) onto (AgNPs –AC) 11 3.4.1 Measurements .15 3.4.2 Data analysis 15 PART IV RESULTS AND DISSCUSSION 16 4.1 Characterization of the nano-activated carbon 16 4.2 Effect of impregnation ratio (AgNPs/AC) on Cr(VI) adsorption capacity .18 4.3 Effect of pH .20 4.4 Effect of contact time 21 4.5 Effect of adsorbent dose 23 4.6 Effect of initial Cr(VI) concentrations 24 4.7 Adsorption isotherm 25 4.8 Adsorption kinetics of AgNPs-AC 31 PART V CONCLUSION .35 REFERENCES 36 v LIST OF FIGURES Figure 4.1 SEM image of (a) AC and (b) AgNPs-loaded activated carbon (AgNPsAC), EDS spectra of (c) AC and (d) AgNPs-loaded activated carbon (AgNPs-AC) 17 Figure 4.2 XRD graph of (a) activated carbon from coconut shells (AC) and (b) AgNPs 2% - loaded activated carbon (AgNPs-AC) 18 Figure 4.3 The effect of the impregnation ratio on chromium adsorption at concentration of 10 mg/L, adsorbent dose: 10 mg AgNPs-AC/25mL Cr6+ solution, Contact time=60 and Temp: 250C 19 Figure 4.4 Effect of pH on the removal of Chromium ion [Cr]=10mg/L, Contact time=60 min, adsorption dose=10mg/25mL, Temp (25C±20C) 21 Figure 4.5 Effect of Contact Time on the Removal of Chromium ion [Cr]=10 mg/L; adsorbent dose=10mg/25mL; pH=4;Temp (25C±20C) 22 Figure 4.6 Effect of adsorbent dose on the removal of Chromium ion [Cr] =10mg/L: Contact time=180 min: pH=4: Temp (25±2oC) 24 Figure 4.8 Adsorption isothermal equilibrium prediction of Cr(VI) onto AgNPs-AC at contact time = 180 min, Ag-AC dose = 20 mg/25mL, initial pH: 4, Temp: 250C) 30 Figure 4.9 Kinetics model of Cr(VI) adsorption onto AgNPs-AC (Co: 10mg/L; adsorbent dosage: 20 mg/25 mL, initial pH: 4, Temp: 250C) 33 vi LIST OF TABLES Table 1: Levels of daily chromium intake by humans from different routes of exposure Table 2: Adsorption isothermal parameters and correlation coefficients of Langmuir, Freundlich and Temkin models for sucrose adsorption on Chromium 31 Table 3: Calculated kinetic parameters of models for adsorption of Chromium onto AgNPs-AC .34 vii PART I INTRODUCTION 1.1 Research rationale Chromium, named for its multicolored compounds, is a transition metal, number 24 in the periodic table of elements This element is found in combination, mainly in chromite ores, and, even if in lower abundant amounts, as crocoites (PbCrO4) and chrome ochre (Cr2O3) Cr is a major element that exists primarily in two different oxidation states, hexavalent and trivalent These oxidation states are denoted as Cr(VI) and Cr(III), respectively The rarely found naturally occurring element has zero oxidation, Cr(0), other oxidation states of Cr are not stable and therefore, are not found in the natural environment Cr(VI) is more flexible than Cr(III) and dificult to remove in water (Elisabeth L Hawley et al, 2004) This chromium (VI) detoxification leads to increased levels of chromium (III) (ATSDR, 1998) Air emissions of chromium are predominantly of trivalent chromium, and in the form of small particles or aerosols (ATSDR, 1998) and (SAIC.PM, 1998) The most important industrial sources of chromium in the atmosphere are those related to ferrochrome production Ore refining, chemical and refractory processing, cementproducing plants, automobile brake lining and catalytic converters for automobiles, leather tanneries, and chrome pigments also contribute to the atmospheric burden of chromium (U.S Environmental Protection Agency, 1998) The general population is exposed to chromium (generally chromium [III]) by eating food, drinking water and inhaling air that contains the chemical The average daily intake from air, water, and food is estimated to be less than 0.2 to 0.4 micrograms (µg), 2.0 µg, and 60 µg, respectively (ATSDR, 1998) Dermal exposure to chromium may occur during the use of consumer products that contain chromium, such as wood treated with copper dichromate or leather tanned with chromic sulfate (ATSDR, 1998) Occupational exposure to chromium occurs from chromate production, stainless-steel production, chromium plating, and working in tanning industries; occupational exposure can be two orders of magnitude higher than exposure to the general population (ATSDR, 1998) People who live in the vicinity of chromium waste disposal sites or chromium manufacturing and processing plants have a greater probability of elevated chromium exposure than the general population Several technologies have been applied to remove Cr(VI) from aqueous solutions including precipitation, reverse osmosis, ion exchange, filtration, sand filtration, chemical reduction/oxidation, electrochemical precipitation, membrane filtration, solvent extraction, and electrochemical deposition and adsorption (ChiChuan-Kan, 2017) Adsorption is an effective and low cost method Particularly, the problem of chromium pollution in water resources is causing concern in major cities and industrial parks; therefore, it is necessary to have a method to remove Cr from the water environment In this study, Cr was treated by adsorption with the adsorbed material is activated carbon coconut shell 1.2 Research's objectives The purpose of this study was to load silver nanoparticles into activated carbon deriving from coconut shell and application for removing chromium from aqueous solution Research on finding the appropriate impregnated rate, evaluation of appropriate conditions for adsorption, including: pH, sorption time, adsorbent dosages reasonably problematic in addition to less than very poor adsorption characteristics (Shafique et al., 2012) Experimentally it was determined that extent of gas adsorption varies directly with pressure and then it directly varies with pressure raised to the power 1/n until saturation pressure Ps is reached Beyond that point, the rate of adsorption saturates even after applying higher pressure Thus, the Freundlich adsorption isotherm fails at higher pressure Temkin Model The derivation of the Temkin isotherm assumes that the fall in the heat of sorption is linear rather than logarithmic, as implied in the Freundlich equation The adsorption experiment data were analysed by Temkin isotherm model in the linearised form The isotherm studied by Temkin and Pyzhev (Temkin and Pyzhev, 1940) comprises a factor that covers the adsorbate–adsorbent interactions explicitly By overseeing the exceptionally high and low concentrations of adsorbate, the model assumes that the heat of adsorption (function of temperature) of all molecules in the layer would reduce linearly rather than logarithmic with coverage owing to interactions between adsorbate and adsorbent This isotherm assumes that the adsorption is regarded as a uniform distribution of binding energies up to some maximum energy It is expressed as follows: = () *+, -'( ) ) = /) -'( ) ) (4) Temkin isotherm contains a factor that clearly shows the interactions between the adsorbent and adsorbate In Temkin isotherm, it is assumed that the adsorption 29 temperature of all molecules decrease when the surface of the adsorbent is more covered Fig 4.8 provides a typical adsorption isotherm plot of qe against Ce In this study, we applied several commonly adsorption isotherm models to describe the chromium adsorption onto AgNPs-AC They are the Langmuir (Equation 1,2) Freundlich (Equation 3) and Temkin (Equation 4) models The corresponding parameters of those models are summarized in Table Figure 4.8 Adsorption isothermal equilibrium prediction of Cr(VI) onto AgNPs-AC at contact time = 180 min, Ag-AC dose = 20 mg/25mL, initial pH: 4, Temp: 250C) The adsorption data of chromium onto AgNPs-AC were found to fit well to the Langmuir, Freundich and Temkin models with R2 values of 0.9121, 0.835 and 0.660, respectively However, the Langmuir model could better describe the adsorption 30 behaviors of chromium onto AgNPs-AC when compared with the Freundich and Temkin models The maximum adsorption capacities (qm) of AgNPs-AC from the Langmuir models was calculated to be approximately 35.09 mg/g Moreover, the values of the Freundlich exponent (1/n) < indicated that the systems were favorable Table 2: Adsorption isothermal parameters and correlation coefficients of Langmuir, Freundlich and Temkin models for sucrose adsorption on Chromium Langmuir model qm KL 35.09 0.099 Freundich model R2 KF 1/n R2 0.9121 7.151 0.368 0.835 Temkin model AT bT 3.349 98.492 B R2 0.460 0.660 4.8 Adsorption kinetics of AgNPs-AC Pseudo-First-Order Model The pseudo-first-order adsorption model is defined by Lagergren (Sen, S, 2011) 01 = ( - 1) (5) Where qe and qt are the amounts of AgNPs sorbed at equilibrium and a given time t The pseudo-first-order adsorption rate coefficient is k1 (min-1) Solving the differential equation for boundary conditions, t = 0, qt = 0, t = t and qt = qt, this equation can be expressed in the linear form as: ln(qe – qt) = lnqe – kt (6) Pseudo-Second-Order Model The pseudo-second-order kinetic equation may be expressed as (Mckay et al, 2011) and (Zhang, S, 2015) 31 = 01 – qt)2 ( (7) Using the integration limits employed in the first-order equation, this equation can be written in the following way: = 23 - t (8) In this case, k2 represents the rate constant for pseudo-second-order sorption (g·mg-1 ·min-1) Elovich Model This mathematical model has been widely used in the description of the kinetics of adsorption of a solute in a liquid phase from a solid sorbent The mathematical expression that governs the behavior of this model is (Cortes-Martinez, 2010) 01 = α4 (9) Integrating Equation (7) and using the boundary conditions of the pseudo-firstorder model, the Elovich or Roginsky and Zeldovich equation would be: qt = -'(67) + lnt 5 (10) Where α is the initial adsorption rate (mg·g-1·min) and β the desorption constant (g·mg-1) In this case, β is described in terms of surface area covered and the activation energy derived from the chemisorption by the adsorbent 32 Figure 4.9 Kinetics model of Cr(VI) adsorption onto AgNPs-AC (Co: 10mg/L; adsorbent dosage: 20 mg/25 mL, initial pH: 4, temperature: 250C) In this study, three common kinetic models were applied to describe the chromium adsorption process onto AgNPs-AC, including the pseudo-first order (PFO; Equation and 6) pseudo-second order (PSO Equation and 8) and Elovich (Equation and 10) models The correct application of such selective models was discussed in detail by Vu et al (2017) The calculated kinetic parameters in the pseudo-first order, pseudo-second order and Elovich models are shown in Table According to the linear regression coefficient (R2), the dynamics of chromium adsorption fit well to all three models As shown in Table 3, the pseudo-first order and pseudo-second order models provided excellent correlation coefficients (R2 = 0.8374 and 0.9116, respectively) with the experimental data compared to the Elovich model The calculated qm value from the 33 pseudo-first order and pseudo-second order model was very close to the experimental data (14.73 and 16.75 mg/g) These results proved that the experimental data followed well the pseudo-first order and pseudo-second order models and both models could describe the adsorption kinetics of chromium onto AgNPs-AC (Fig 4.9) The fitting of experimental data using pseudo-first order and pseudo-second order models suggest that adsorption of chromium onto AgNPs-AC is controlled by chemisorption, which involves valence forces through sharing or exchange of electrons (Pathania et al 2017) Thus, the kinetics of chromium adsorption on AgNPs-AC was well described by the pseudo-first order and pseudo-second order models Table 3: Calculated kinetic parameters of models for adsorption of Chromium onto AgNPs-AC Preudo-First oder qm,cal K1 R2 (mg/g) 14.73 Preudo-Second oder qm,cal Elovich qe,exp K2 R2 α β R2 (mg/g) 2.003 0.9116 1.798 0.297 0.9597 15.67 (mg/g) 0.038 0.8374 16.75 34 PART V CONCLUSION Silver nano-activated carbon (AgNPs-AC) is a interesting capacitate for Cr(VI) removal from aqueous solutions The Cr(VI) adsorption process of AgNPs-AC was highly depended on pH of solution The pH of for adsorption of Cr(VI) was the optimum condition in this study The results also showed that there was an 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Environmental Science and Management Student name Ha Thi Lan Anh Student ID DTN 1454290001 Thesis title Chromium (VI) removal from aqueous solution by using Silver nano- activated carbon Supervisor(s)... + NaNO3 Loading of Silver Nanoparticles onto the Activated Carbon Granules o Activated carbon (AC): AC derived from activated carbon coconut shells, purchased from Tra Bac Company, Vietnam o Silver. .. coefficients From this study, it can be concluded that AgNPs-AC is an interesting adsorbent, saving, easy to remove Cr (VI) from the aqueous solution Keywords Silver nano- activated carbon, Chromium,