Development of Nano-Hydroxyapatite Embedded Gelatin

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Development of Nano-Hydroxyapatite Embedded Gelatin Biocomposite for Effective Cr(VI) Removal Venkatrajan Gopalakannan, and Natrayasamy Viswanathan Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b01224 • Publication Date (Web): 22 Nov 2015 Downloaded from http://pubs.acs.org on November 28, 2015

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Industrial & Engineering Chemistry Research

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Development of Nano-Hydroxyapatite Embedded Gelatin Biocomposite for Effective

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Cr(VI) Removal

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Venkatrajan Gopalakannana, Natrayasamy Viswanathanb*

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a

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009, Tamilnadu, India

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b

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Dindigul – 624 622, Tamilnadu, India.

Department of Chemistry, Velammal College of Engineering and Technology, Madurai - 625

Department of Chemistry, Anna University, University College of Engineering - Dindigul,

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*

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E-mail address: [email protected] (N. Viswanathan)

Corresponding author. Tel.: +91-451-2554066 (O); fax: +91-451-2554066.

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1 ACS Paragon Plus Environment


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ABSTRACT

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A biocompatible sorbent namely nano-hydroxyapatite embedded gelatin (n-HApGel)

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composite was developed by in-situ precipitation method. The synthesized biocomposite was

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subjected to the removal of hexavalent chromium from aqueous solution in batch mode. The

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FTIR, SEM and EDAX techniques were adapted for investigating the functional groups, surface

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morphology and elements present in the sorbent. The crystalline nature of the composite was

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carried out using XRD studies. TGA analysis gives the thermal stability of the composite. The

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size and shape of the composite was studied using TEM analysis. The sorption process was

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optimized by various influencing factors viz., contact time, adsorbent dosage, temperature, pH

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and competing ions for maximum sorption. The equilibrium data was fitted to Freundlich,

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Langmuir and Dubinin – Radushkevich (D-R) isotherms. Thermodynamic parameters indicate

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the nature of Cr(VI) sorption and a possible sorption mechanism was proposed for the removal

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of Cr(VI) using n-HApGel biocomposite. The suitability of the biocomposite at field conditions

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was tested with field water taken in a nearby industrial area.

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Keywords: Nano-hydroxyapatite; Gelatin; Biocomposite; Hexavalent chromium; Isotherms

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1. INTRODUCTION

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The heavy metals enter into the environment by both natural and anthropological

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activities. Unlike the organic pollutants, metallic pollutants released into the environment tend to

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persevere indefinitely, circulating and finally accumulating throughout the food chain thus

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posing a serious threat to human beings and animals. Chromium is one such naturally occurring

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element, exists with two different oxidation states viz., Cr(VI) and Cr(III). 1 The non- toxic form

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of chromium i.e., Cr(III) is supposed to be essential in glucose metabolism in mammals2

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whereas, Cr(VI) is toxic to both plant and animal cells.2,3 The World Health Organization

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(WHO) has also proposed 0.05 mg/L as maximum dischargeable limit for Cr(VI) of the

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industrial effluents in the surface water.4 Although the discharge cannot be controlled due to its

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widespread application, the only way to avoid its toxicity is to adopt cleaner technology for its

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efficient removal.

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Numerous methods are available for the removal of heavy metals which includes

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adsorption, ion-exchange, precipitation, reduction and membrane processes.5 Among them,

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adsorption process is more preferable due to its easy operation, selectivity and cost effective.6 A

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wide range of novel sorbents like nano ziroconia,7 silica,8 dolamite,9 activated carbon,10

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hydroxyapatite,11 etc., have been subjected for chromium adsorption studies. Amongst which

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hydroxyapatite (HAp) is one of the most promising materials for chromium removal due to its

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low cost, easy availability and higher adsorption capacity. The main reason for employing n-

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HAp is due to its chemical composition and crystal structure.11 Despite of its advantages, it has

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its own limitations viz., poor strength, low stability and also causes pressure drop at field

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conditions.12 In order to overcome such bottle-necks, recently numerous research works have

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been formulated to synthesize biocomposite by dispersing hydroxyapatite over biopolymers like



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chitosan,13 chitin,14 alginate,15 gelatin,11,16,17etc., which possess an enhanced the adsorption

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capacity.

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The biocomposite materials of organic/inorganic origin were extensively studied due to

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their excellent biocompatibility and biodegradability. Gelatin (Gel) is a polypeptide obtained by

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thermal degradation of collagen, a protein widely present in biological connective tissues.

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Gelation of collagen has been widely used in industrial, food science, pharmaceuticals and

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medical applications.18-21 Gelatin possess many chemical groups which have strong affinity to

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metal ions. Therefore, hydroxyapatite, gelatin and modified gelatin were extensively used for

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adsorption of heavy metals from aqueous solution.22-26

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The present investigation concentrates on the synthesis of biocompatible n-HApGel

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composite and subjected to Cr(VI) adsorption by batch process. The instrumental techniques

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like FTIR, TEM, SEM with EDAX, TGA and XRD studies were adapted to characterize the

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synthesized biocomposite. For optimizing maximum sorption capacity (SC), influence of

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contact time, pH and in the presence of other competing ions on chromium adsorption were

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studied. Various adsorption isotherms viz., Freundlich, Langmuir, and Dubinin – Radushkevich

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were formulated. To know the nature of the sorption, thermodynamic parameters were

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calculated and the possible mechanism for the sorption of Cr(VI) onto n-HApGel composite was

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proposed. The suitability of the composite at field conditions was also tested.

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2. EXPERIMENTAL

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2.1. Materials

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Gelatin, potassium dichromate, calcium nitrate, 1,5- diphehylcarbazide, ammonium

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hydroxide, ammonium phosphate and all other reagents used are of AR grade purchased from

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Merck (Germany). The synthetic solutions were prepared using double distilled water.


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2.2. Synthesis of n-HApGel Biocomposite n-HApGel biocomposite was prepared by in situ precipitation method. About 7 g of

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gelatin was added to 100 ml of ammonium dihydrogen phosphate solution and the contents were

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stirred constantly using a magnetic stirrer. When the solution attained homogeneity 5 % of

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calcium nitrate solution was added drop wise with constant stirring for 30 min. After 30 min,

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ammonium hydroxide solution was added in drops to the above mixture followed by vigorous

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stirring. The addition was done until the pH of the solution reached 8 wherein a white slurry of

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n-HApGel composite starts to deposit. The contents were then kept aside for 48 h and after that

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it was filtered and dried in hot air oven. The dried composite was crushed to fine powder using

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ball mill (IKA, Germany). The fine composite powder was sieved to get uniform size and then

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used for chromium sorption studies.

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2.3. Sorption Experiments

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Chromium sorption tendency of the synthesized biocomposite was studied by adapting

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batch mode. During these studies, initial Cr(VI) concentration was fixed at 100 mg/L. Cr(VI)

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solution (100 mg/L) was prepared by dissolving 0.2828g of AR grade potassium dichromate in

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1000 mL distilled water. About 50 mL of this solution was taken in a flask and 0.1g of sorbent

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material was added. The flask was then kept in a thermostated shaker at 200 rpm and the

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supernatant solution was tested for residual Cr(VI) concentration. Since sorption depends on

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various factors like contact time, pH, presence of competing ions and temperature, influence of

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such factors were studied. The solution pH was adjusted using 0.1 M HCl/NaOH solution.

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Temperature studies were conducted for synthesized n-HApGel biocomposite at three different

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temperatures 30, 40 and 50 °C with different initial Cr(VI) concentration viz., 80, 100, 120 and



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140 mg/L. The dosage of the sorbent, volume of Cr(VI) solution and all other parameters were

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maintained as constant.

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Sorption capacity was calculated by using the mass balance equation

Sorption capacity (SC), q =

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C 0 − Ce V (mg / g ) W

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where C0 and Ce are initial and final concentration of Cr(VI) ions (mg/L), V is the volume of

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Cr(VI) solution taken (mL) and W is the weight of the sorbent used for sorption (g).

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2.4. Analysis

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Sorption experiments were conducted using thermostated shaker (REMI, India).

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Chromium concentration was determined by using UV-Visible spectrophotometer –

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Spectroquant – Pharo 300 (Merck, Germany) at 540 nm. The pH of the medium was measured

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using Thermo Orion Benchtop multiparameter kit (VERSA STAR 92) using pH electrode.

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2.5. Characterisation Studies

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The changes in surface morphology of the sorbent before and after Cr(VI) sorption

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process, was investigated using scanning electron microscope (SEM- VEGA3 TESCAN). Also

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elemental analysis on the surface of the sorbent was carried out using EDAX (Bruker Nano

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GMBH, Germany). To find the functional groups of n-HApGel composite, fourier transform

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infrared spectroscopy (JASCO-60 plus) was adopted and the spectrum was recorded between

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the range 400 – 4000 cm-1. For phase identification of the nano composite, X-ray diffraction

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studies was carried out by using XRD-X’per PRO model-PANalytical instrument. Further the

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synthesized composite was subjected to TGA(SDT Q600 V20.9 Build 20 model) to explore the

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phase transitions. The size and shape of sorbents were measured by Transition Electron

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Microscope (TEM) images. TEM images were recorded using TEM CM 200 (PHILIPS) model.

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To investigate the surface area of the sorbent, surface analyser NOVA 1000 model in nitrogen 6 ACS Paragon Plus Environment

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atmosphere was used. pH drift method was followed to determine the pH at zero point charge

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(pHzpc) of the composite.27

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2.6. Computational Analysis

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The Microcal Origin (Version 8) was used for the computational work and to check the

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best of the fit, regression correlation coefficient and chi square analysis (χ2) were used.

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3. RESULTS AND DISCUSSION

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3.1. Characterization Studies

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n-HApGel composite was characterized by various instrumental techniques. Fig. 1

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depicts the FTIR spectrum of gelatin, n-HApGel composite and Cr(VI) sorbed n-HApGel

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composite. In FTIR spectra of gelatin, three characteristic bands at 1641, 1462 and 1242

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cm-1corresponds to amide I, amide II and amide III groups of gelatin respectively.28 In n-HApGel

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composite, bands at 1035 cm-1 and 566 cm-1 might be due to the asymmetric stretching and

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bending modes of PO43- respectively. On the other hand a band at 3411 cm-1 could be due to the

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presence of hydroxyl group, broadening of which reveals the chromium sorption. In the FTIR

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spectra of Cr-loaded n-HApGel composite, shift in almost all the above characteristic bands,

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indicates the sorption of Cr(VI) onto the biocomposite.29

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Fig.1, 2& 3 - Insert here SEM pictures of n-HApGel composite and chromium sorbed n-HApGel composite are

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shown in Fig. 2a and 2b respectively. The first one reveals the well discrete structure of n-

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HApGel composite whereas the latter shows the changes on the surface of n-HApGel composite

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due to chromium sorption. Fig. 2c and 2d depicts the EDAX spectrums of n-HApGel composite

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and chromium sorbed n-HApGel composite. The presence of chromium peak in EDAX spectrum

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of chromium sorbed n-HApGel composite confirms the chromium sorption onto the composite.



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The crystalline nature of the composite was tested by XRD analysis. Fig. 3a shows the

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XRD patterns of n-HAp particles, n-HApGel and Cr-sorbed n- HApGel composites. XRD

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pattern of n-HAp shows peaks at 2θ = 25.92°, 32.1° and 39.81°. These peaks were also found in

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the XRD pattern of n-HApGel biocomposite indicating that, there is no changes in the crystalline

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structure of n-HAp.30 The changes in the XRD pattern of chromium sorbed n-HApGel

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composite suggests the structural changes have occurred after adsorption of Cr(VI) onto the

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sorbent.

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Fig. 3b gives TGA curve of the biocomposite. During thermal analysis, two major weight

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losses were observed. The first weight loss is around 9.8% at 200 - 511o C and second weight

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loss around 13.5% at 720 - 770o C were due to structural decomposition of gelatin and banish of

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carbon dioxide respectively. 31 The specific surface area of synthesized n-HAp particles and

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n-HApGel composite were analyzed under nitrogen atmosphere and found to be 102 and 130

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m2/g respectively.

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The size and shape of sorbent was measured by TEM and given in Fig. 4. The particles of

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n-HApGel composite possess cylindrical rod like shape with homogeneous microstructure and

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tend to agglomerate to form a uniform nano material. Fig.4, 5 & 6- Insert here

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3.2. Effect of Contact Time To quantify the variability of the synthesized n-HApGel composite on contact time with

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the Cr(VI) solution, about 0.1 g of the adsorbent was added in a flask containing 50 mL of 100

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mg/L Cr(VI) solution and the contact time was varied between 10 to 100 min. The effect of

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contact time on SC of n-HAp and n-HApGel composite are shown in Fig. 5a. From the figure it

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is clear that n-HApGel composite attains equilibrium at 80 min, whereas n-HAp attains at 50


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min. The SCs of n-HAp and n-HApGel composite were found to be 10.24 and 17.40 mg/g

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respectively. Since n-HApGel composite possess high SC, it is considered for further

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investigation and its contact time was fixed as 80 min.

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Along with chromium analysis, filtrate is also analyzed for other ions like hydroxide,

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phosphate, calcium, etc. From the analysis it is evident that the filtrate contains hydroxide ion

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that is due to leaching of OH- ions from the sorbent material.

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3.3. Effect of Dosage

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Adsorption process always depends on the dosage of the sorbent in the medium. To

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optimize n-HApGel composite dosage, the sorption experiments were carried out by varying the

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dosage of n-HApGel composite between 0.05 to 0.150 g with 100 mgL-1initial chromium

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concentration and maintaining all other parameters constant. From Fig. 5b, it can be inferred that

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sorption capacity of the sorbent increases with increase in dosage of n-HApGel composite. This

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could be due to, increase in the availability of the reactive sites. After 0.1 g dosage of the

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composite material, SC does not exhibit any remarkable increase, which may be due to the

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saturation during sorption process and this particular 0.1 g dosage will be sufficient for the

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maximum sorption of chromium onto the composite.32-34 Hence the optimum dosage of the

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sorbent was fixed as 0.1 g and the same was maintained for further investigations.

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3.4. Influence of pH

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The pH of the medium plays an important role on the sorption process. To explore the

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influence of pH on the removal of Cr(VI) by the synthesized n-HApGel composite, sorption

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experiments were conducted over the pH range between 3 to11. The pH of the medium was

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adjusted by using 0.1 M HCl/NaOH solution. About 0.1g of the composite was added to 50 mL

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of Cr (VI) solution with 100 mg/L as initial chromium concentration and maintaining all other



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parameters as constant. From the results depicted in Fig. 6a, it is coherent that maximum Cr(VI)

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removal was obtained in acidic pH rather in basic pH. The SC tends to decrease with increasing

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pH level. It is important to remember that Cr(VI) can exists in various forms in different pH

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levels that includes Cr2O72- , HCrO4¯, CrO42-, HCr2O7¯ and H2Cr2O7. When the pH of the

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medium is between 2-6 the predominant species will be Cr2O72- and HCrO4¯ and under this

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acidic pH range, adsorbent will be more protonated facilitating the sorption of negatively

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charged Cr(VI) ions. 35 In addition to this, -NH group present in the polymeric matrix may also

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get protonated and it electrostatically attracts the anionic HCrO4¯ ions. Further Cr(VI) species

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may also get reduced to Cr(III) by its interaction with atoms like nitrogen and oxygen present in

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n-HApGel composite.16, 17, 36 This is due to the fact that Cr(VI) gets reduced in the presence of

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electron donor atoms like nitrogen and oxygen.37, 38 On the other hand, if the pH of the medium

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crosses 6 the most prevailing species of Cr(VI) is Cr2O72-. At this higher basic pH range,

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hydroxyl ion present in the solution competitively binds in the active centers of the sorbent and

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leads to decrease in the SC, as a result sorbent offers a repulsive force towards the chromate

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anion. Therefore, pH of the medium influences the SC of n-HApGel composite i.e., SC is higher

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at acidic pH rather than basic pH. The equilibrium pH of the solution was found to be neutral in

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all the pH ranges.

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The pHzpc study of the materials was carried out by pH drift method and is shown in Fig.

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6b. The pHzpc of n-HAp was found to be 7.70 and it was shifted to 6.62 for the synthesized n-

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HApGel composite. The presence of lower SC in alkaline medium can be elucidated by the fact

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that above pH 6.62 (pHzpc value), the sorbent surface acquires negative charge in alkaline pH and

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hence there is repulsion between the negatively charged composite surface and chromate ion.

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3.5. Influence of Competing Ions

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The normal water contains Ca2+, Mg2+, Na+, Cl−, NO3¯, HCO3¯ and SO42− and the

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influence of these competing ions towards Cr(VI) sorption on n-HApGel composite was studied.

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The sorption experiments were carried out at solution pH of 4.62, with initial concentration of

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competing ions as 200 mg/L, 100 mg/L initial Cr(VI) concentration and by maintain all other

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parameters as constant. Fig. 7 depicts the influence of competing ions on SC of the composite. It

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is clear from the figure that HCO3¯ and SO42− have commendable influence on the SC, whereas

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other ions do not have remarkable influence. This may be due to the similarity in size of HCO3¯

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and SO42− ions with HCrO4¯ ions, which may compete with the active sites of the composite.

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3.6. Sorption Isotherms To establish equilibrium between adsorbed Cr(VI) ions onto n-HApGel composite (qe)

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and unabsorbed Cr(VI) in the solution (Ce), three isotherms namely Freundlich,39 Langmuir40

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and Dubinin-Redushkevich 41were adopted. In such investigations, initial Cr(VI) ion

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concentration was varied as 80, 100, 120 and 140 mg/L at various temperatures like 30, 40 and

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50 °C.

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Table 1 - Insert here The linear plot of log qe vs. log Ce of the composite indicates the applicability of

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Freundlich isotherm and the results were listed in Table 1 . The constructive conditions for

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adsorption was revealed from adsorption intensity i.e., 1/n values, which lie between 0 and l and

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that of n values between 1and 10. Increase in adsorption capacity kF along with temperature

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suggests the endothermic nature of the sorption process. Similarly, applicability of this isotherm

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was further established from higher r values.



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Langmuir adsorption isotherm illustrates the ideal adsorption and administers monolayer

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homogeneous adsorption. The slope and intercept of the plot between Ce/qe vs. Ce gives the

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values of Qo and b respectively. From Table 1 it is apparent that increase in Qo and b values

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indicates the endothermic nature of the sorption process. For different temperatures RL values

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were calculated and also listed in Table 1. These values lie between 0 and 1 explicating the

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favorable condition for the sorption process. Similarly higher r values indicate the applicability

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of Langmuir isotherm.

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Dubinin - Radushkevich isotherm was used to determine the type of adsorption for the

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removal of metal ion from aqueous solution by adsorption. The values of the adsorption capacity

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Xm (mg/g), ε is Polanyi potential and k (mol2/kJ2) the constant related to adsorption energy were

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listed in Table 1. The values of k and Xm were computed from the slope and intercept of the plot

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ln qevs ε2. The higher values of r validate the applicability of D-R isotherm. The values of the

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Polanyi potential, ε lies between 1 and 8 indicating that sorption follows mainly electrostatic

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attraction.

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Among the isotherms, to spot the best fit isotherm model for the sorption of Cr(VI) onto

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n-HApGel composite, chi-square analysis was used and is given in Table 1. It is evident that by

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comparing all the chi square values, Langmuir isotherm possesses low chi square values. So the

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best fit isotherm model for the sorption of Cr(VI) on n-HApGel composite is Langmuir isotherm.

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A comparison of SC of various adsorbents reported in the literature with n-HApGel

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biocomposite has been listed in Table 2.

272 Table 2 & 3 - Insert here 273 274


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3.7. Thermodynamic Behavior and Mechanism of Sorption Process

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The various thermodynamic parameters like ∆H°, ∆S° and ∆G° were calculated to

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understand the nature of sorption. Table 3 shows the values of ∆Hº and ∆Sº which were attained

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from the slope and intercept of the plot of lnKo against 1/T. The spontaneous nature of Cr(VI)

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sorption onto the n-HApGel biocomposite can be revealed from the negative values of ∆G°. The

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positive value of ∆Hº stipulates that the sorption process was endothermic. Throughout the

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Cr(VI) sorption process, randomness between solid-solution interface increases which is evident

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from the positive value of ∆Sº.

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The possible mechanism of chromium sorption onto n-HApGel biocomposite was

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depicted in Fig. 8. The removal of Cr(VI) on the biocomposite was governed by electrostatic

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attraction, ion exchange and reduction. The cation (Ca2+) present in the biocomposite

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electrostatically attracts the negatively charged chromate ions. In addition to this electron

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donating atoms like nitrogen and oxygen present in the sorbent reduces Cr(VI) into less toxic

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Cr(III). Further the hydroxyl ion present in the biocomposite may also get exchanged with the

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negatively charged HCrO4¯ ions from the aqueous solution.

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Table 4 &Fig. 8 - Insert here 3.8. Application of synthesized biocomposite at field conditions The efficiency of the synthesized n-HApGel composite at field conditions was tested by

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collecting field water sample taken in a nearby industrial area. About 0.1 g of the composite was

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added to 50 mL of the field water sample and the contents were shaken for a fixed time at room

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temperature by maintaining all other parameters as constant. The results obtained are presented

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in Table 4. The results showed that there was a significant reduction in Cr(VI) concentration. It is



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evident from the results that the composite may be effectively employed for removing Cr(VI)

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ions from water.

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4.Conclusions

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The biocomposite n-HApGel was synthesized and successfully removes Cr(VI) ions from

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aqueous medium by showing enhanced SC than n-HAp particles. n-HApGel biocompatible

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nano-composite was characterized using various instrumental techniques viz., FTIR, TEM,

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XRD, TGA, SEM and EDAX analysis. The sorption process was influenced by pH, the

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maximum sorption was recorded at acidic pH rather in basic. The presence of competing ions,

305

like HCO3¯ and SO42- decreases the sorption capacity of n-HApGel biocomposite. The

306

observation of various thermodynamic parameters indicates that the sorption process is

307

endothermic and spontaneous. The sorption of Cr(VI) onto the n-HApGel biocomposite follows

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Langmuir isotherm and the mechanism of sorption was mainly due to electrostatic attraction

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coupled reduction and ion exchange.

310 311 312 313 314 315 316 317 318 319


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FIGURE CAPTIONS Fig.1. FTIR Spectra of Gelatin, n-HApGel Composite and Cr(VI) Sorbed n-HApGel Composite Fig.2. SEM Images of (a) n-HApGel Composite and (b) Cr(VI) Sorbed n-HApGel Composite, EDAX Spectra of (c) n-HApGel Composite and (d) Cr(VI) Sorbed n-HApGel Composite. Fig.3. (a) XRD Pattern of n-HAp Particles, n-HApGel Composite and Chromium Sorbed n-HApGel Composite (b) TGA Curve of n-HApGel Composite. Fig.4. TEM Images of n-HApGel Composite @ a) 100 nm and b) 50 nm Fig.5. (a) Effect of Contact Time on the SC of n-HApGel Composite. (b) Effect of Dosage on the SC of n-HApGel Composite. Fig.6. (a) Influence of pH (b) pHzpc Study Fig.7. Influence of Competing ions on the SC of n-HApGel Composite. Fig.8. Possible Mechanism of Cr(VI) Removal by n-HApGel Composite.



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Table 1 Isothermal Studies of Cr(VI) Sorption onto n-HApGel Composite

Isotherms

Freundlich

Langmuir

30 °C

40 °C

50 °C

1/n

0.773

0.600

0.597

n

1.2936

1.6663

1.6758

kF (mg/g) (L/mg)1/n

12.714

13.856

14.204

r

0.9482

0.9715

0.9715

sd

0.0048

0.0028

0.0028

χ2

0.0010

0.0005

0.0006

Qo(mg/g)

18.828

19.001

19.120

b (L/g)

0.2326

0.2732

0.3088

RL

0.2118

0.1862

0.1683

r

0.9999

1.0000

1.0000

sd

0.0184

0.0084

0.0119

0.0003

0.0002

0.0001

kDR(mol /J )

2.2013E-08

1.8211E-08

1.4473E-08

Xm(mg/g)

6.7376

6.8007

6.8927

ε (kJ/mol)

4.7659

5.2399

5.8776

r

0.9818

0.9709

0.9775

sd

0.0055

0.0065

0.0050

χ2

17.9349

18.3901

18.6838

χ

2 2 2

Dubnin-Radushkevich

Temperature

Parameters


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Table 2 Comparison of Adsorption Capacities of Various Adsorbents towards Cr(VI) Removal. Adsorption capacity (mg/g)

Reference

n-HApGel composite

17.40

Present study

CTAB-Silica Gelatin composite

16.60

17

Gelatin-Yeast

500.00

26

Bituminous activated carbon

10.53

42

Dolochar

2.10

43

Modified montmorillonite

11.97

44

Silica gel/chitosan composite

3.50

45

Cerium cross linked magnetic alginate beads

14.29

46

n-HAp/Chitosan composite

3.40

47

n-HAp/Chitin composite

2.80

47

Magnetite

10.60

48

Montmorillonite/magnetite nano particles

15.30

48

Nano Silica-Aspergillus ustus

526.3

49

Nano Silica -Fusarium verticillioides

416.7

49

Nano Silica -Pencillium funiculosum

243.9

49

Gelatin-Grafted Yeast biosorbent

1000

50

Activated carbonC-Fe3O4

588.24

51

Activated carbon-Fe3O4-Yeast

769.23

51

Adsorbent



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Table 3 Thermodynamic Parameters of Cr(VI) Sorption onto n-HApGel Composite Thermodynamic Parameters

Temperature

∆G˚ (kJ mol-1)

30 °C

-3.40

40 °C

-3.47

50 °C

-3.55

∆H˚ (kJ mol-1)

1.18

∆S˚ (kJ K-1 mol-1)

0.01


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Table 4 Application of n-HApGel Biocomposite at Field Conditions

Water quality parameters

Before treatment

After treatment

Chromium(mg/L)

1.07

Nil

pH

7.54

7.41

Cl- (mg/L)

1810

1050

Total Hardness (mg/L)

1100

840

Total Dissolved Solids (mg/L)

4800

1900



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Fig. 1.Gopalakannan and Viswanathan


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a

b

c

d

Fig.2.Gopalakannan and Viswanathan



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Fig.3.Gopalakannan and Viswanathan


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Fig.4. Gopalakannan and Viswanathan 29 ACS Paragon Plus Environment


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Fig.5. Gopalakannan and Viswanathan


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Fig.6.Gopalakannan and Viswanathan 31 ACS Paragon Plus Environment


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Development of Nano-Hydroxyapatite Embedded Gelatin Biocomposite for Effective Cr(VI) Removal Venkatrajan Gopalakannana, Natrayasamy Viswanathanb* a

Department of Chemistry, Velammal College of Engineering and Technology, Madurai - 625 009, Tamilnadu, India b

Department of Chemistry, Anna University, University College of Engineering - Dindigul, Dindigul – 624 622, Tamilnadu, India. *

Corresponding author. Tel.: +91-451-2554066 (O); fax: +91-451-2554066. E-mail address: [email protected] (N. Viswanathan)

For Table of Contents Only


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Development of Nano-Hydroxyapatite Embedded Gelatin

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