BIBECHANA Vol. 21, No. 3, December 2024, 221-232 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher: Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University) Biratnagar Biosorption study of Cr (VI) from the aqueous solution using chemically modified biomass of a newly isolated edible mushroom waste Gopal Gautam Khatri1, Manish Baskota1, Anita Chand1, Samjhana Bharati2, Dasu Ram Paudel1∗ 1Department of Chemistry, Tri-Chandra Multiple Campus, Tribhuvan University, Kathmandu 44600, Nepal 2Department of Chemistry, Amrit Campus, Tribhuvan University, Kathmandu 44600, Nepal. ∗Corresponding author: Email: dasu.paudel@trc.tu.edu.np Abstract Despite some physiological role in human body, some metals, like hexavalent chromium, have no recognized biological benefit and are poisonous above tolerance limits. For the first time, a widely available Pleurotus sajor caju (fungus) biomass was studied for the Cr (VI) adsorption from an aqueous solution involving physisorption, and chemisorption. Using the batch adsorption method, sorption experiments were conducted, and sorption parameters such as pH, contact time, adsorbent dose, and starting metal ion concentration were studied. The sorbent material was shown to remove up to 91.67% of the Cr (VI) at a pH value of 2. It was discovered that the maximum adsorption (qmax) was 239.98 mg/g. The Freundlich model was adopted for the equilibrium adsorption isotherm for Cr (VI). The biosorption kinetics was ascertained by fitting pseudo-first order and pseudo-second order kinetic models for the experimental data and the pseudo-second order model was found to better describe the data. The interaction of metal ions with the carboxyl, hydroxyl, and carbonyl groups present in biomass is primarily involved in metal ions uptake. This demonstrated the potential application of mushroom residues as a low-cost and promising bio-sorbent. Keywords Bio-adsorbent; Heavy metals; Adsorption; Batch study; Water security. Article information Manuscript received: January 22, 2024; Revised: May 29, 2024; Accepted: June 7, 2024 DOI https://doi.org/10.3126/bibechana.v21i3.62097 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 221 http://nepjol.info/index.php/BIBECHANA dasu.paudel@trc.tu.edu.np https://doi.org/10.3126/bibechana.v21i3.62097 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 222 1 Introduction The aquatic environment is facing exceptional chal- lenges and become one of the primary global con- cerns because of abandoned water pollution and unintended water security [1]. Aquatic pollution knowingly affects the water quality, visibility, and water reaction mechanisms including the lack of dis- solved oxygen, biodegradation processes, and pho- tosynthesis [2]. Heavy metals, dyes, and hazardous pigment effluents discharged from different sources like battery, electroplating, textile, pesticide, fertil- izer, cosmetics, etc. contaminate the water sources which pose a warning to public health and ecosys- tems [3]. As opposed to organic contaminants, most of the heavy metals are toxic, carcinogenic, non-biodegradable and accumulate in living tissues through the food chain, causing severe damage of internal organs [4]. Thus, great attention regarding the elimination of toxic heavy metals, dyes, pig- ments, etc. is required using a novel, low cost, and feasible technology and material. Specifically, Chromium is considered as a major pollutant in aquatic environment owing to its ex- tensive use in leather, electroplating, ceramics, and other industries [5]. Mostly, the Cr(VI) forms like HCrO4 -, CrO4 2-, and Cr2O7 2- are strongly oxidiz- ing and are predominantly found in surface water and aerobic soils species [6,7]. The Cr(III) is essen- tial element for the human body and other living organism however the Cr(VI) is 5-10 times toxic than Cr(III) and is classified among the top pol- lutants and listed as the 16th dangerous contami- nant [8,9]. Due to high solubility, the Cr(VI) intake typically occurs through contaminated food, leak- age, sea foods, skin or respiratory tract and can easily enters in stomach, kidney, and liver. The health issues related to Cr(VI) include the risk of lung, nasal, sinus cancer, ulcer, anemia, damage to sperm, detriment to the male reproductive system, asthma, abdominal pain, eye irritation, etc. [10,11]. The adverse health effects of Cr (VI) compelled us to solve the problem by finding a suitable method of removal from aquatic environments. Remedi- ation of heavy metals from aqueous solutions is a topic of significant interest in environmental re- search. Among many, reverse osmosis, flotation, ac- tivated carbon adsorption, ion exchange, chemical reduction, precipitation, electrodialysis, and some traditional methods are in common practice to re- move heavy metals from water and wastewater [12]. These are just a few examples of the methods used for the remediation of heavy metals from aqueous solutions. Researchers continue to explore innova- tive technologies and materials to improve the effi- ciency and cost-effectiveness of heavy metal removal processes. However, the mentioned approaches are typically costly and ineffective, especially at low metal ion concentrations between 1 and 100 mg/L [13]. Adsorption is a widely used method for the re- moval of heavy metals from water having low con- centration of metal ions. Materials like activated carbon, clay minerals, zeolites, and biosorbents are commonly used for adsorption due to their high sur- face area and adsorption capacity [14]. The solid- phase byproduct of biomass pyrolysis, biomass car- bon, has gained attention as a possible material to treat wastewater due to its rich functional group sites and better developed pore structure. Re- searchers have developed cutting-edge techniques including physicochemical activation, metal load- ing, and organic/inorganic modification to bring biochar from the lab to the commercial sector. These techniques have produced good results in terms of increasing specific surface area, optimizing the structure of the pore layer, and changing func- tional groups, all of which significantly improved the pore structure and surface functional groups [15]. Consequently, it is important to design a stable, earth-abundant, inexpensive, and highly effective adsorbent for water purification and heavy metal decontamination process, such as bio- adsorbent [16]. A known biotic mechanism cannot dissolve toxic heavy metals from water. Biosorption is a very common physiochemical mechanism that involves the adherent of atoms, ions, or molecules of dissolved solids from liquid to the surface of solid materials derived from organic sources [17]. Principally, the biosorption process involves a sim- ple chemistry where the heavy metal ions in aque- ous solution bound on the surface of an adsorbent due to an imbalance between two environments creating a driving force to be adsorbed onto ad- sorbent. The process continues till phase equilib- rium is established between the amount of solid- bound adsorbate species and its fraction left be- hind in the solution [18]. Activated carbon, sea- weed, microorganisms, fermented waste, and some other generated biomasses are only a few examples of the many diverse types of bio-sorbent sources that are defined by their wide source, cheap cost, and effective adsorption capability [16–19]. More- over, mushroom-based biomasses are potent for the bioremediation of several heavy metals, dyes, or- ganic pollutants, etc. The hemicellulose fungal cell wall, chitin, chitosan, polyuronide, polyphosphates, lipids, and proteins are the primal components of the mushroom fungus that portray the superior metal binding abilities [20,21]. Studies demonstrate the use of mushrooms and fungal biomass as effec- tive biosorbents for the removal of various heavy metals from aqueous solutions and researchers are continuously exploring novel approaches and tech- nologies to enhance the efficiency and sustainability Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 223 of heavy metal remediation processes using mush- rooms [22–24]. Specifically, for the bioremediation of hexavalent chromium, fungal derived adsorbents are widely used, demonstrating effective removal from aque- ous solutions. The mushroom substrate shows that it has an exceptional ability to adsorb Cr (VI) from water. The fungus species' cell wall contains chitin, which contributed to the likely binding of the Cr (VI) ions. Fungal cell walls are made up of 80–90% heteropolysaccharides, proteins, lipids, polyphos- phates, and inorganic ions that act as adhesive ma- terial to create the walls. A common component of fungal cell walls that has the capacity to com- plex metal ions is chitin. Also many polysaccha- rides found in fungal cell walls are crucial for metal binding. It has also been discovered that some func- tional groups, specifically carboxyl groups, have the capacity to bind metal ions [25]. The potential of mushroom-derived waste biomaterials for the ad- sorption and extraction of heavy metals that are harmful from wastewater is interesting. Significant recycling potential is also accessible for the waste fungal biomass adsorbent that is created. following five cycles of adsorption and regeneration. Up to 85.5% of Cr (VI) ions are still able to be eliminated with good effectiveness [26]. Through a series of batch adsorption experi- ments, the study explores the effectiveness of oys- ter mushrooms (Pleurotus platypus) for the re- moval of Cr(III) and Cr(VI) from aqueous solutions. The results demonstrate that the ligand exchange process and electrostatic force of attractions are the main causes of the adsorption processes [27]. Other several mushroom(fungus) species were re- ported to show great efficacy for the bioremedia- tion of Cr(VI). Aspergillus carbonarius performed well with 92.43% removal of Cr(VI) [28]. In this work, we derived modified Pleurotus sajor caju waste-derived biomass and focused on the efficacy towards biosorption of toxic heavy metal, Cr(VI), from water bodies. The im- pact of modified and raw Pleurotus sajor caju waste-derived biomass to remove Cr(VI) from syn- thetic aqueous solution was accessed. The 0.1 M NaOH modified Pleurotus sajor caju waste-derived biomass powder showed an increased sorption ca- pacity of positively charged metal ions (Cr+6) onto its surface than raw biomass possibly due to the in- teraction of metal to hemi cellulosic cell wall compo- nents. As a result, the addition of NaOH in biomass enhances their ability of metal binding and mechan- ical strength as well. The sorption property was explored by analyzing the effects of contact time, adsorbent dose, pH, adsorption isotherm, starting concentration, and batch kinetics. The SEM, EDS, and FT-IR analysis describe the surface structure and basic chemical groups in the biomass. Hence, this work suggests and found a strategic function- alization of Pleutorous sajo-coju waste as potential bio-adsorbent to amplify the basic understanding of adsorption in a real aquatic environment. 2 Materials and Methods 2.1 Materials All the chemicals (Sulphuric acid, Buffer tablets, Potassium dichromate, 1,5-diphenyl carbazide, Ni- tric acid, Sodium hydroxide, etc) of analytical grade were purchased from Thermo Fisher Scientific In- dia. 1000ppm stock solution of potassium dichro- mate, 0.1 N nitric acid, 5N sulphuric acid, 2N nitric acid, 0.1M & 2N sodium hydroxide, 0.25% DCPI so- lution and buffer solutions (pH-4.0,7.0 & 9.2) were prepared in different volumes. 2.2 Experimental 2.2.1 Preparation of raw and modified ad- sorbent The mushroom was washed, shade dried, then ground to a mess size of 250 microns. A part of pow- ered mushroom underwent 0.1M NaOH treatment, followed by three hours of reflux at 80°C. The pH of the final product was then kept neutral by wash- ing with distilled water and adding nitric acid. For two hours, the mixture was then dried in an oven set at 80°C. The products were then used for the adsorption studies and FTIR was used to confirm the extent of modification [29,30]. Modifying bio-adsorbents enhanced adsorption capacities, but it will increase the adsorbents' cost. Therefore, a cost-benefit analysis is required. The modifying chemicals used in this study may cause impacts on the environment so the proper discharge procedures were followed. 2.2.2 Determination of λmax and calibration Various volume of working Cr(VI) solution contain- ing 20mg/mL were taken in 25 mL volumetric flask, acidified with 1 mL of 5 N H2SO4, followed by ad- dition of 1 mL of 0.25% of DCPI solution and re- maining volume with distilled water. The absorp- tion spectra of pink colored Cr(VI)-DPCI complex were recorded against blank solution. Among var- ious absorption spectra, λmax was recorded at 530 nm, using calibration curve [31,32]. 2.2.3 Batch adsorption study An Erlenmeyer flask is pipetted with a known con- centration of metal solution that has been pH- adjusted, and the predetermined quantity of ad- sorbent is then added. The flask is shaken for the Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 224 specified amount of time to ascertain the concentra- tion of adsorbate. Adsorbate adsorption is depen- dent on a number of factors, including pH, contact time, adsorbent dosage, metal solution concentra- tion, etc. One of these parameters was changed while keeping the others fixed in order to under- stand the adsorption mechanism. The equilibrium adsorption amount (qe) and the percent metal up- take by adsorbent were expressed [32,33]. qe = (Ci− Ce)V w mg/g (1) where, qe is the amount of metal ion adsorbed per unit mass of adsorbent, w is weight of adsor- bent (g), Ci is Initial concentration of adsorbent dose (mg/L), Ce is equilibrium concentration of ad- sorbate (mg/L), v is volume of adsorbate. The ratio of the adsorbate ion concentration be- fore and after adsorption to the initial concentration of metal ions in aqueous solution determines the ad- sorbate removal percentage. Removal percentage(R) = Ci− Ce Ci x100 % (2) 2.2.4 Adsorption isotherm The amount of adsorbate adsorbed per mass of adsorbent and the quantity of unabsorbed adsor- bate remaining in the solutions at equilibrium time are related by a curve known as the adsorption isotherm. The most significant isotherms for ana- lyzing the adsorptive behavior of an adsorbate and an adsorbent are the Langmuir and Freundlich ad- sorption isotherms. 2.2.4.1. Langmuir adsorption isotherm The linear form of this isotherm is represented by the expression 1 qe = 1 qm + 1 qmKLCe (3) where, qe is maximum adsorption of bio-sorbent at equilibrium (mg/L), qm is theoretical monolayer saturation capacity(mg/L), KL is Langmuir equi- librium constant (L/mg). Langmuir constant qm and KL can be obtained as slope ( 1 qm ) and intercept ( 1 qmKL ) respectively from the linear plot of (Ce qe ) Vs Ce. By utilizing a dimensionless constant separation factor or equi- librium parameter, the fundamental properties of the Langmuir adsorption isotherm can be used to estimate the affinity between the biosorbent and the biosorbate. RL =1/1 +KLC i. (4) 2.2.4.2. Freundlich adsorption isotherm The Freundlich adsorption isotherm assumes a heterogeneous adsorption surface and active sites with different energy. This isotherm can be ex- plained by equation 5 [34]. qe = KFC 1/n e (5) where, KF is Freundlich constant (L/g), n = Freundlich exponent (g/L). The value of these factors affects the isotherm's curvature and steepness, while the value of n reveals the adsorbate's affinity for the adsorbent. This isotherm's linear form is written as: log (qe) = log (KF ) + 1 n log (Ce) (6) 2.2.5 Adsorption kinetics . 2.2.5.1. Pseudo first order kinetic model The pseudo first order kinetics proposed by Lagergren for adsorption analysis can be express in equation 7 [35]. dqt dt = k1 (qe − qt) (7) where, qe is amount of Cr(VI) per gram on the surface of adsorbent at the equilibrium(mg/g), qt is amount of Cr(VI)per gram on the surface of ad- sorbent at time ‘t’(mg/g), k1 is equilibrium rate constant of pseudo-first order kinetics. After integration and applying boundary condi- tion, t = 0 to t = t, qt = 0, and qt = qt the linear form of the equation (7). loq (qe − loq (qt − qt) = loq qe − k1t 2.303 (8) K1 is calculated from the linear plot of log (qe- qt) against time. 2.2.5.2. Pseudo second order kinetic model The pseudo second order rate equation for ad- sorption analysis [36]. dqt dt = k2(qe − qt) 2 (9) After integration and boundary condition qt = 0 at t=0, qt = qt at t = t equation (9). t qt = 1 k2q2e + 1 qet t (10) where, k2 is equilibrium rate constant for pseudo second order kinetics, k2 and qe can be calculated from the graph of t/qt against t. Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 225 2.2.6 Spectrophotometric methods for the determination of Cr (VI) DPCI method is quite suitable for the determina- tion of Cr(VI) in aqueous solution. The absorbance of the solution measured at maximum wavelength is 530 nm. 2.2.7 Material characterization The Fourier transform Infra-red (FTIR) spec- troscopy was done at the Central Department of Chemistry, Tribhuvan University, Kathmandu. The Spectra of RPSC and MPSC were obtained with a BRUKER spectrometer model, using potassium bromide (KBr) pellet method. The surface mor- phologies of MPSC and RPSC samples were char- acterized by using Field emission scanning electron microscope (FE-SEM, Model: Supra 40 V P instru- ment Zeiss Co., Germany) and energy dispersive X-ray spectroscopy (EDS) based elemental compo- sition in the Center for University-Wide Research Facilities (CURF) of Jeonbuk National University, South Korea. 3 Result and Discussion By adopting a most generalized and simple hy- droxyl functionalization technique, the waste of edi- ble mushroom Pleutorous sajo-coju was prepared as an active biomass for heavy metal (Cr+6) removal from aqueous solution (Scheme 1, details in exper- imental section). On optimizing different physico- chemical parameters such initial pH, initial adsor- bate concentration, contact time, adsorbed dosage, and desorption research, the sorption of Cr (VI) in an aqueous solution was investigated based on raw and functionalized PSC. Scheme 1:Schematic representation showing preparation and modification of bio-adsorbent from Pluoro- tous sajor-caju (fungus), application for removal of Cr (VI) from aqueous solution and characterization. 3.1 Maximum absorbance and calibration curve study The maximum absorption wavelength for Cr (VI) obtained at 530 nm was used to prepare calibration curve, shown in Figure (1 a, b). 3.2 Effect of contact time for Cr (VI) DPCI complex formation The effect of contact time on adsorption of Cr (VI) at initial concentration of 50 mg/L were studied. The Figure 2 showed the experimental data where Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 226 a rapid uptake of metal ion occurs initially and ab- sorbance value was nearly constant from 0 to 20 minutes, the absorbance value within 20 minutes was calculated using DPCI solution. The relation- ship between time and absorbance is shown in Fig- ure 2. 3.3 Effect of pH for absorption of Cr (VI) on to MPSC and RPSC Figure 3 illustrates how pH affects the adsorption of Cr (VI) onto RPSC and MPSC. In the instance of RPSC, removal of Cr (VI) was found to be re- duced as pH increased; the highest removal value was shown to be at 1.0, which is an optimum pH for RPSC. However, the highest removal value for MPCS was shown to be 2.0, and this pH is optimum for MPSC. 3.4 Effect of contact time for adsorption of Cr (VI) onto RPSC and MPSC The batch adsorption of a 20 mg/L metal solution with a 25 mg adsorbent was studied by assessing the impact of contact time over different time peri- ods ranging from 10 minutes to 360 minutes. The impact of contact time on the adsorption of Cr (VI) onto RPSC and MPSC is shown in Figure 4. Ad- sorption was discovered to be expanding as time value has increased. Figure 1: (a) Determination of max for Cr (VI)-DPCI complex (b) calibration curve. Figure 2: Effect of time on Cr (VI)-DPCI complex formation. Figure 3: Effect of pH on Cr (VI) adsorption by RPSC and MPSC. Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 227 Figure 4: Effect of contact time for the adsorption of Cr (VI) onto RPSC and MPSC. 3.5 Effect of initial Cr (VI) ion concentra- tion For MPSC, the quantity adsorbed increased from 11.61 mg/g to 201.90 mg/g, whereas for RPSC, the amount adsorbed increased from 13.82 mg/g to 204.12 mg/g. The adsorption increased from lower concentration to higher concentration ranges (20 mg/L to 500 mg/L). These results demonstrate that, as the amounts of adsorbent increases, so does adsorption. The effects of the initial adsorbate con- centration for RPSC and MPSC are shown in Fig- ure 5. Figure 5: Adsorption isotherm of Cr (VI) onto RPSC and MPSC. 3.6 Batch isotherm studies The Freundlich and Langmuir isotherms exhibited a linear relationship with Cr (VI) adsorption onto MPSC and RPSC. Figures 6 (a) and (b) illus- trate respectively, the Langmuir isotherm and the Freundlich isotherm whose R2 value indicates that Freundlich isotherm is best fitted over Langmuir isotherm. This result indicates that Freundlich isotherm has greater applicability. The insight into the sorption favorability in terms of correlation co- efficient indicates the active sites of MPSC were dis- persed throughout and the ions are adsorbed chem- ically on the surface. Figure 6: (a) Langmuir isotherm and (b) Freundlich isotherm plot for the adsorption of Cr (VI) onto RPSC and MPSC. Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 228 3.7 Batch kinetic modeling The kinetic data for Cr (VI) adsorption onto MPSC and RPSC was studied using pseudo-first-order and pseudo-second-order kinetic models. The compar- ative plot of these models is represented in Fig- ures 7 (a) and (b), respectively. From the kinetic plots for the adsorption of Cr (VI), it was found that the value of the correlation coefficient (R2) for the pseudo-second-order kinetic model was higher (close to one) than that of the pseudo-first-order. The results of the experimental data were better described by pseudo-second-order kinetics. This ki- netic model signifies the adsorption behavior of ad- sorbent across the complete range. Figure 7: Pseudo (a) first and (b) second order kinetic model for the adsorption of Cr (VI) onto RPSC and MPSC. 3.8 Effect of adsorbent dose The effect of the adsorbent dose for the adsorption of Cr (VI) onto MPSC and RPSC, was studied at room temperature by varying the adsorbent amount from 25 mg to 200 mg which indicates that the ad- sorbent dose is directly proportional with the ad- sorption yet showed constant value of the % ad- sorption beyond 100 mg for MPSC and 160 mg for RPSC, respectively. In addition to this, % adsorp- tion was remarkably higher in case of MPSC over RPSC for the same doze of adsorbent. Figure 8 shows the effects of adsorbent dose for the adsorp- tion of % of Cr (VI). 3.9 FTIR analysis FTIR analysis was performed to investigate the sur- face functional groups of MPSC and RPSC whose spectra have been shown in Figure 9 (a) and 9 (b), respectively. The graph of MPSC indicated the presence of -OH, C=O, N=N=N, N=C=S, C=N, N-O, etc., which are responsible for the adsorption of Cr (VI). Compounds containing these functional groups have enough ability to bind chromium as they contain double bond active sites. Figure 8: Effect of adsorbent dose for the adsorp- tion of Cr (VI) onto RPSC and MPSC. Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 229 Figure 9: FTIR spectra of (a) RPSC and (b) MPSC. 3.10 FE-SEM and EDS analysis Figure 10 displays the FESEM analysis of the adsorbent samples both before and after adsorp- tion along with EDS mapping and EDS spectrum. Prior to adsorption, the FESEM images at differ- ent magnitudes for MPSC revealed a porous struc- ture and the presence of more free sites (Figure 10 A-C). The high magnification image of MPSC in Figure 10C indicates the distinctive porosity, and awful rough surfaces with broken edges thus providing valuable sites for metal ion adsorption on the surface of adsorbent. After adsorption, the sur- face morphology of sorbent MPSC (Figure 10D) showed some changes that signify the effective ad- sorption of metal ions on the surface of the adsor- bent. The morphological change as a result of the accumulation of Cr (VI) ions on MPSC led to the smooth and brighter surfaces might be due to in- teraction of functional group of sorbents with tar- geted metal ions. This revealed that a higher con- centration of Cr (VI) had been adsorbed using the bio-sorbent also confirmed from the EDS elemen- tal mapping obtained from the FESEM. The post- adsorption EDS pattern of MPSC (Figure 10E-I) revealed characteristic colour mapping images for carbon, nitrogen, oxygen, and chromium. More- over, the EDS spectrum and the elemental distribu- tion in Figure 10J clearly depicts the significant amount of chromium and other element revealing the potency of bio-adsorbent for efficient removal of toxic metal from aqueous solution. Overall, the rough surface of MPSC has a considerable effect on the capacity for adsorption [37]. Figure 10: FE-SEM image of (a, b, c) MPSE, (d) MPSC after adsorption and (e, f, g, h, i) FESEM-EDS colour mapping of MPSC, (J) EDS spectra of MPSC and corresponding atomic composition.. Gopal Gautam Khatri et al./ BIBECHANA 21 (2024) 221-232 230 4 Conclusion This study provides promising evidence for the use of Pleurotus sajor-coju as the potent source of a new adsorbent due to high abundance and low cost- ing procedure. Modified Pleurotus sajor-coju was found to be more effective adsorbent than raw one, for the removal of Cr (VI). FTIR analysis con- firms the presence of azide, thiocyanate, alcohol, ni- tro, sulphonyl chloride and oxime groups on NaOH modified Pleurotus sajor-coju (MPSC) which are responsible for adsorbing Cr (VI) from aqueous so- lution. The mass of the adsorbents were reported to be amorphous, however certain peaks displayed the crystallinity of cellulose. Additionally, the SEM analysis of the surface morphology revealed a rough, uneven surface with a distinct dark area of pores and voids. These circumstances favor the adsorp- tion of metals. Various results illustrate that the adsorption of Cr (VI) increase with the increase in contact time, concentration of the solution and ad- sorbent doze. The mechanism of adsorption is bet- ter described by pseudo-second order kinetics with the Freundlich isotherm giving the best fit over the Langmuir isotherm. Acknowledgment We would like to acknowledge the CURF, Jeonbuk National University, South Korea (for FESEM and FESEM-EDS analysis), Department of Chemistry, Tri-Chandra Multiple Campus (for instrumenta- tion), Central Department of Chemistry, Kirtipur (for sample characterization). Conflict of interest The authors have no financial and other conflict of interest. References [1] M.P. Adhikari, M.R Neupane, and M. Kafle. 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Introduction Materials and Methods Materials Experimental Preparation of raw and modified adsorbent Determination of max and calibration Batch adsorption study Adsorption isotherm Adsorption kinetics Spectrophotometric methods for the determination of Cr (VI) Material characterization Result and Discussion Maximum absorbance and calibration curve study Effect of contact time for Cr (VI) DPCI complex formation Effect of pH for absorption of Cr (VI) on to MPSC and RPSC Effect of contact time for adsorption of Cr (VI) onto RPSC and MPSC Effect of initial Cr (VI) ion concentration Batch isotherm studies Batch kinetic modeling Effect of adsorbent dose FTIR analysis FE-SEM and EDS analysis Conclusion