Facile Synthesis Of Activated Carbon From Natural Bio-Mass “Zea Mays” For Adsorptive Removal Of Hexavalent Chromium (Cr(VI)) From Industrial Waste Water

Sahu D, Tripathi TK, Padhy H, Patnaik A, Panda C and Nahak PK

Published on: 2024-02-29

Abstract

Removal of Hexavalent chromium [Cr(VI)] from wastewater using biochar through adsorption, is commonly acknowledged as a simple, economical, and highly selective method. This study examined in detail the adsorption of hexavalent chromium from waste water by activated carbon (AC) made from biomass Zea mays(Corn cob), a readily available biomass, were used to create the AC in an economical manner. Owing to the distinct multi-layered and honeycomb porous structure created by the activation and delignification processes, the resulting activated carbonised Zea mays has an abundance of oxygen-containing functional groups, increasing meso-pores, and an increased surface area. A thorough investigation was conducted into the adsorption behaviors of wastewater containing Cr(VI) in the range of 100 to 300mg/L on biomass. To support the formation, morphology, structure and suitability the synthesized biomass are examined using FTIR, SEM-EDS, and XRD analytical techniques. The adsorption properties of the biomass were investigated through batch adsorption experiments that varied adsorption factors such as temperature, pH, dose concentration, and contact time with different initial concentrations. The optimal adsorption of hexavalent chromium [Cr(VI)] obtained was 99.962% with an ideal adsorbent dosage of 40gm/l, pH of 3.0, contact time 50 min, temperature 40oC, maximum initial concentration 300mg/l, which comply with the government of India's discharge standard of 0.1mg/L for hexavalent chromium. Besides the adsorption, the Freundlich and Langmuir isotherms were determined to be suited for the task based on their kinetic properties. The Langmuir and Freundlich isotherms are closely resembled by the absorption data set. The Cr(VI) capture by Zea mays is facilitated by the synergistic contributions of the capillary force, electrostatic attraction, chemical complexation, and reduction action. Therefore, it was found that the biomass Zea mays utilised in this study was an efficient material for treating waste water that contained chromium.

Keywords

Waste water Zea mays Isotherms Adsorption Hexavalent chromium

Introduction

Hexavalent chromium [Cr(VI)] is a highly oxidizable and toxic persistent pollutant which when absorbed in the body, it will suppress cell metabolism, lead to cancer, and create gene mutations [1,2]. Due to toxic properties and ability to accumulate through the food chain, extensive pollution of the aquatic environment by industrial waste water containing of Cr(VI) is a serious environmental concern [3,4,5,6]. Therefore, one of the main areas of research in the field of water environmental protection has always been the processing of Cr(VI) wastewater. The main source of chromium pollution is the industrial processes that are manufacturing steel, Iron, lather, metal finishing and some inorganic chemical production industries as well [7,8].

Many techniques have been developed to remove Cr(VI) from polluted water in order to address the aforementioned issues. These consist of adsorption [9], ion exchange [10], membrane filtration [11], and chemical precipitation [12]. Adsorption in particular is regarded as a simple, economical, and highly selective technique. Thus far, a number of high-performance adsorbents for the removal of Cr(VI) have been developed, including carbon materials (also known as biochar), magnetic materials, and porous materials derived from biomass [13]. Of these, Activated carbon which is made by pyrolyzing agricultural waste at temperatures above 700°C is thought to be a promising option because of its large specific surface area (SSA), exceptional adsorption capabilities, low cost, and plentiful resources [14]. Nevertheless, owing to the limited porosity and surface activity of pristine AC, it is challenging for it to meet the need for higher adsorption capacities. Enhancing the pore structure, surface chemistry, and specific surface area requires the development of modification technologies, which are extremely important [15]. Despite the fact that there are nine valency states for chromium, ranging from -2/+6, Cr(VI) have significant environmental implications. In addition, to the best of our knowledge, no much reports have yet focused on the application of the delignified strategy for the preparation of Zea mays carbon materials for the adsorption of Chromium metals. Many attempts have been made to use adsorption techniques to remove hexavalent chromium from water [16,17] but at a low pH of 1-3, the maximum Cr(VI) of was eliminated using pseudosecond order kinetics [18]. In addition carbon impregnated with potassium hydroxide forms a broad pore size distribution; carbon impregnated with zinc chloride creates microspores.

Both activation methods produced activated carbon with a large specific surface area and pore size primarily made up of mesopores and micropores. The benefits of the chemical activation method include easy recovery, a broad range of applications, and good activated carbon treatment efficiency. Several chemical reagents are used in the chemical activation process, the most widely used ones being potassium hydroxide, phosphoric acid, zinc chloride, and potassium carbonate [13]. As bioadsorbents are environmentally friendly, their credibility has grown significantly in recent years. Sulphuric acid was used to chemically activate raw adsorbent that was made from agricultural waste. For the purpose of a chromium adsorption study, AC made from tamarind wood was chemically activated with zinc chloride. The initial chromium content and the adsorbent dosage were the main factors influencing the removal percentage, which is governed by the diffusion mechanism. In order to successfully adsorb Cr6+, Yang et al. synthesised AC from long a seeds using a NaOH chemical treatment. The optimum adsorption was observed at a pH value of 3, and kinetically, it is satisfied with the Langmuir isotherm model using a pseudo second order equation. The pH has a significant impact on how well the adsorbent removes chromium. At pH 2.5, Yadav et al. discovered the ideal adsorptive efficiency of 80% [19]. The two species of Cr(VI) at lower pH values of 2-4 are hydro chromate ions, HCrO4-(approximately 85%), and di-chromate ions, Cr2O72- (approximately 11%), where HCrO4- predominates. There are species at a medium pH range of 4-6 as well, including HCrO4- and Cr2O72-, of which Cr2O72- is dominant; at a high pH range of 6-10, there are only CrO42- species [20-21]. The pyrolysis of combetrum quadrangular resulted in carbonised carbon, which was subsequently chemically activated with 45% phosphoric acid. It was discovered that the Cr(VI) adsorption followed a pseudo-second order kinetic at pH 1-2 and fitted with Langmuir and Freundlich isotherms well [22].

Here in this study abundantly available maize cob, scientifically known as Zea mays, has been selected in this study as an adsorbent material for the removal of hexavalent chromium from industrial waste water. Following the removal of the seeds, the raw corncob was removed from the corn plant and activated mechanically, chemically and thermally to prepare AC for the adsorption of chromium from industrial waste water. The wastewater was produced artificially and had chromium content of 100mg/l to 300 mg/l, much like wastewater from chrome plating. Subsequently, the AC synthesised from Zea mays was used in the adsorption studies to determine the adsorption behaviour. In order to examine the adsorption behaviour of chromium on the adsorbent material, characterization studies involving XRD, SEM-EDS, and FTIR, were conducted for the raw AC and adsorbed AC. The optimized conducive parameters including contact time, adsorbent dosages, pH, temperature etc. are obtained through batch experiment and the resultant adsorption/removal of [Cr(VI)] from waste water containing a maximum of 300mg/l found is satisfying the requirements of waste water disposal standard by EP Act 1986.

Experimental

Materials and Methods

The Cob of the maize plant by its scientific name as Zea mays was used to make adsorbent materials. The seeds of the corn were removed and the raw cobs were gathered, sun dried, cut into pieces, and ground into tiny grains. Potassium dichromate (K2Cr2O7) and sodium hydroxide pellet (NaOH) were provided by NICE chemicals, ethanol (C2H5OH) sulphuric acid (H2SO4), and 1,5-diphenylcarbazide (DPC) were provided by Merck Life Science, India. Without any additional purification, all analytical-grade chemicals were utilized in this investigation exactly as they were. A milli-Q water stock solution of Cr(VI) (1000 mg/L) was made using potassium dichromate (K2Cr2O7). After that, it was diluted to create solutions with the correct Chromium concentrations to match with the industrial waste water (100mg/l, 200mg/l, and 300mg/l).

Preparation of Activated Carbon (AC) from Zea mays

The maize cob collected from corn plant by removing the seeds were sun dried to remove all the water content inside. The cobs then made into granular peaces and dried it for 24hours at 105ºC in an oven. The dried granules then grinded until the particle sizes were between 1 to and 105μm and sieved for the desired size. The adsorbent material was then heated to 105ºC for 24h in an oven. Afterwards, it was chemically activated using H2SO4 in 3:4 to produce carbonized material. After being carbonized, the materials were cleaned with deionized water to achieve a neutral pH before being dried once more at 105ºC in the oven for another 24h. It was grinded and filtered using mechanical sieve to collect a particle size of 105μm. Subsequently, the adsorbent material was activated by heating in a muffle furnace at 750ºC for 30 minutes covered with a lid. To prevent moisture contact, the desired AC was stored in a desiccator. Figure 1 depicts the detailed Schematic diagram for the preparation of AC of maize cob which was prepared through thermal and chemical activation.

Figure 1: Synthesis of Activated carbon of adsorbent material from Zea mays.

Characterization of Adsorbent Material

The morphology and structure of AC were characterized before and after Cr(VI) adsorption by SEM analysis using Tescan Mira-III field emission scanning electron microscopy at 500X to 200 kX magnification. Powder X-ray diffraction was performed using Bruker-D8 advance diffract meter with Cu Kα 1.5418 Angstroms for the samples AC before adsorption and after adsorption. As functional group has high affinity to Cr(VI), ATR-FTIR spectrums was performed using a Bruker Alpha-II ATR-FTIR Spectrophotometer and range from 4000cm-1 to 500cm-1.

Batch adsorption Experiments

Adsorption of Cr(VI) on adsorbent surface is primarily influenced by different parameters including pH, initial Cr(VI) concentration, contact time, stirring speed and temperature. Here, milli Q water was used to dissolve a calculated and weighted amount of K2Cr2O7 in order to create the industrial wastewater sample synthetically. The solution was made up to the appropriate mark with distilled water using 28.3mg, 56.6mg, and 84.9mg of AR grade K2Cr2O7 in a 100ml volumetric flask for the initial concentrations of 100mg/L, 200mg/L, and 300mg/L, respectively. Following the adsorption process, the solution was filtered, and an aliquot sample was taken out of the bottles containing the filtered sample. After complexation with 1,5 diphenyl carbazide in an acidic medium, the concentration of remaining Cr(VI) ions in the biosorption medium was measured spectrophotometrically at 540nm using a double beam UV/vis spectrophotometer (Shimadzu, Japan, Model SPECORD 200) [23]. The Cr(VI) concentrations in the effluents were obtained spectrophotometrically by acid reaction with 1,5-diphenylcarbazide. The colored complex of Cr(VI) was read at 540nm using a spectrophotometer.

The following equations were used to determine the adsorbed amount of Cr(VI) ion and the percentage removal of Cr(VI).

% Adsorption=

Where, Co (mg/L) is Cr(VI) concentration, Ce(mg/L) is the Cr(VI) concentration left in solution after equilibrium, qe indicates the adsorbed amount of Cr(VI), V(L) is the volume of the solution and W is the mass of the adsorbent [24].

Adsorption Kinetics

To get deep into the adsorption mechanism of biomass adsorbent and Cr(VI) adsorbate, we have to studied the adsorption kinetics. The experimental data is subjected to pseudo first order and pseudo second order analysis. The kinetic model of pseudo first and second order is articulated in the following equation 3 and 4 respectively [25]:

C0 is the initial concentration, Ce and Ct are the equilibrium concentration and concentration after time t.K1 (min-1) and K2 (g/mg.min) is the rate constant of pseudo first order and pseudo second order adsorption respectively. The determination coefficient is R2, and the adsorption capability at equilibrium is shown by qe(mg/g) and at time t by qt(mg/g).

Desorption Analysis

Five consecutive cycles of biosorption and desorption were carried out after adsorption at peak conditions to assess the reusability of biosorbent. Each dry powder from the adsorbed AC powdered sample was combined with 100ml of 0.1N NaOH solution, which was made by combining 6g of NaCl with 1litre of distilled water. Following a 7-day desorption operation at 300°C and 250 rpm stirring of the solutions, aliquot samples were collected in sample bottles and sent for Cr(VI). Using a complexion with 1,5-diphenilcarbazide, a PC-based UV-Visible double beam spectrophotometer was used to measure the concentration of hexavalent chromium.

Result and discussion

FTIR Analysis

As can be seen in Figure 2, the recorded ATR-FTIR spectrums at a range of 500–3500cm-1 in AC reveals a variety of surface functional groups, along with changes in position and surface reactions both before and after adsorption. Following adsorption, the peaks at 3335cm-1 show the presence of hydroxyl groups (-OH), and the peak's slight shift shows the development of hydrogen bonds with the adsorbent [26]. The peak at 2692cm-1 was attributed to methyl asymmetric C–H stretching. Peak at 2138cm-1 and 2359cm-1 shows the existence of C-C vibrations of alkyne group. The existence of strong band at 1551cm-1 is characterized for carbonyl (C=O) stretching. Another strong band at 1115cm-1 may shows the C-H stretchings of methyl groups. Further the weak peaks at lower wave number 829 and 694cm-1 was attributed to the band of aliphatic alkane. The loading of chromium on the AC surface causes the characteristic peaks to exhibit a shift in frequency value because the functional group has a high affinity for Cr(VI). It details the functional groups are involved in the binding of metals and the adsorption of Cr(VI) on the AC surface

Figure2: FT-IR data of activated carbon of Zea mays before and after adsorption of Cr (VI) SEM-EDS Analysis.

SEM-EDS Analysis

The surface morphology of the adsorbent Zea mays was observed before and after adsorption of Cr(VI) using the scanning electron microscope (SEM) technique. Using Tescan Mira-III field emission scanning electron microscopy at 500X to 200 kX magnification, SEM pictures were captured. The samples were sputter coated with a small layer of platinum to help with charge dissipation during FESEM imaging. In an argon environment, the sputter coater (Eiko IB-5 Sputter Coater) was used. After that, the coated samples were moved to the SEM specimen chamber to obtain the images and the micrographs are depicted in Figure 3. As shown in the figure 3 (a) and (b) the different micrograph surface of Zea mays activated carbon was found to have porous like structure with widely spread pores, plenty of cavities, and irregular, uneven, and rough surfaces like crests and troughs. These crests and troughs serve as reactive adsorption centers which improve the surface area and therefore enhances Cr(VI) adsorption capacity of the adsorbent. The increased pore development and irregularities in porous nature could be attributed to the H2SO4 activation of AC.

Figure. 3: SEM Image of (a) activated carbon (AC) with scale 10μm (b) activated carbon (AC) with scale 5μm (c) AC loaded with Cr(VI) of 300mg/l with scale size 20μm (d) AC loaded with Cr(VI) of 300mg/l with scale size 10μm.

The majority of macropores that are readily identifiable in figure 3b come in a variety of sizes and forms that provided efficient adsorption sites and spaces at different parts of the adsorbent.

The surface morphology of the microspheres changed significantly after adsorption (Fig. 3c, 3d), possibly due to the adsorption of Cr(VI), and the particle surface became incredibly smooth with the appearance of filled pore structure [27]. After adsorption, the pore surfaces are filled with chromium ions which are clearly visible in image as bright white colours which confirmed as existence of Cr(VI) on AC surface. From analysis of EDS spectrum, it showed the presence of Carbon and Oxygen as major elements and Chromium as minor element, in different amounts, in mass and atomic percentages and are given in Table 1.

Table1: Analysis of Carbon, Oxygen and Chromium before and after adsorption.

Sample

Element

Weight %

Atomic %

AC

C

91.2

93.3

O

8.8

6.7

Cr

0

0

AC loading with 300 mg/l of Chromium

C

76.43

82.82

O

20.03

16.29

Cr

3.54

0.89

Figure 4: Atomic fraction and weight fraction of different element resulted from EDS before adsorption [(a), (b)] and after [(c), (d)] adsorption of Cr(VI) on AC of Zea mays.

As shown in the EDS analysis graph Figure 4, AC of Zea mays before adsorption, (4a, 4b) the weight percentages and Atomic % of Carbon, Oxygen, and Cr(VI) were 91.8%, 8.2%, and 0.0% and 93.3%, 6.7% and 0% respectively and after adsorption(4c, 4d) with Cr(VI) solution of 300mg.l-1, the weight percentage of Carbon, Oxygen, and Cr(VI) changed to 76.43%, 20.03%, 3.54 respectively and the atomic percentage of Carbon, Oxygen, and Cr(VI) Changed to 82.82%, 16.29% and 0.89% respectively. The efficient adsorption of chromium on the AC surface is what causes the fluctuation in the percentage of carbon and oxygen. Additionally, the creation of oxygen-containing functional groups like hydroxyl, carboxyl, and carbonyl, which provided additional electrons for the reduction of Cr(VI) to Cr(III), is credited with increasing the amount of oxygen in the AC surface.

XRD Analysis

As depicted in Fig. 5, the powder XRD pattern of AC Zea mays loaded with Cr(VI) of 300mg/l before and after adsorption, exhibited widened diffraction, which is shows the amorphous nature of the pure carbon [28]. In addition, it is noted that the XRD pattern of Zea mays AC loaded with Cr(VI) ions differs in their 2???? value from unloaded AC. This implies that the Cr(VI) ion molecules adsorb chemically without changing the structure of

Figure 5: XRD patterns of AC Zea mays before and after adsorption of Cr(VI).

Impact of different Parameter on Cr(VI) adsorption

For getting optimum conditions of temperature, dosage, contact time, rotational speed, pH adsorption batch experiments are carried out by taking the prepared solutions in 250ml beakers at different pH range(1-9), with different adsorbent dose (10gm/l- 40gm/l) in 1liter of distilled water at different temperatures ranging from 20 to 50ºC for different contact time (10-60min) with stirring speed of 200rpm with an initial solution concentration of 100mg/L, 200mg/L and 300mg/L respectively and the results are tabulated in Table 2. The Cr(VI) analysis in mg/L at different adsorbent dosages at agitational speed 200rpm at optimum temperature of 40ºC are optimized. Then by taking 40g/L as optimum adsorbent dose, adsorption process was carried out at different pH of 1-9 with varying contact time of 10-60min, at temperature of 30ºC with stirring speed of 200rpm for initial solution concentration of 100mg/L, 200mg/L and 300mg/L respectively. From the result we found that at pH3 and contact time of 50minutes, agitational  speed of 200rpm were found 0.02mg/L, 0.05mg/L and 0.07mg/L as Cr(VI) for initial

Table 2: Cr(VI) adsorption analysis at different, initial concentration(IC), contact time(CT), adsorbent doses(AD), pH and Temperature(T).

CT=50min, AD=40gm/l, pH=3, T=40ºC

CT=50min, IC=300mg/l, pH=3, T=40ºC

CT= 50min, IC=300mg/l, T= 40oC, AD= 40gm/l

IC= 300mg/l T=40oC, AD=40gm/l, pH=3

IC= 300mg/l CT= 50min, AD=40gm/l, pH=3

IC(mg/l)

% Adsorption

AD(gm/l)

% Adsorption

pH

% Adsorption

CT(Min)

% Adsorption

 

% Adsorption

100

99.987

20

94.5

1

99.85

10

97.23

25

99.857

200

99.979

30

99.289

2

99.943

20

98.13

30

99.9

300

99.962

40

99.962

3

99.962

30

99.06

35

99.913

 

 

50

99.962

4

99.83

40

99.53

40

99.962

 

 

 

 

5

98.871

50

99.962

45

99.57

 

 

 

 

6

98.6

 

 

50

97.345

 

 

 

 

7

97.43

 

 

 

 

 

 

 

 

8

86.4

 

 

 

 

 

 

 

 

9

84

 

 

 

 

Concentration of 100mg/L, 200mg/L and 300mg/L respectively. The effect of different parameters including initial Conc,(100mg/L to 300mg/L), adsorbent doses(10g/L - 40g/L), pH(1 - 9), contact time(10min-60min) and temp(25ºC-50ºC) have been studied and tabulated in Table 2 and the effects of each parameter at optimum conditions have been shown in Figure 6(a- e)

Effect of Initial Concentration

Figure 6(a) illustrates the variation in initial concentrations, which range from (100mg/L, 200mg/L, and 300mg/L), in the study of the effect of different initial concentrations on adsorption of Cr(VI) at constant optimum conditions (adsorbent dose 40g/L, pH 3, contact time 60min). According to the analysis (Table 2), the percentage of chromium removed has decreased as the original concentration has increased. For all concentrations (100mg/L, 200mg/L, and 300mg/L), the Cr(VI) adsorption was still more than 99.9% under ideal circumstances. The variation in solute concentration in the solution and on the adsorbent surface is mostly responsible for the rise in initial concentration [29].

Figure 6: Impact of (a) Initial concentration (b) pH (c) Adsorption dosage and (d) Contact time (e) Temperature on Cr(VI) adsorption.

Effect of pH

According to the majority of the research reports, the impact of pH on adsorbent adsorption is significant. Low pH values are preferred for the elimination of Cr(VI) using AC. The adsorption of Cr(VI) in the pH range of 2-4 under optimal condition was found to be more than 99% and substantially dropped with a rise in pH, as illustrated in Figure 6(b) and Table 2. The neutralization of negative charges on the adsorbent surface is responsible for the favorable adsorption at low pH. For a higher starting concentration of chromium in the effluent (30mg/L), the ideal pH was determined to be 3. The elimination percentage of Cr(VI) steadily drops with increasing pH, reaching around 84% at pH 9 (figure 6(b) and Table 2). Cr(VI) species in lower pH ranges of 2-4 are hydro chromate ions, or HCrO4-(about 85%), and di-chromate ions, or CrO2-(approximately 11%), where HCrO predominates. There are species at a medium pH of 4-6 as well, including HCrO4- and Cr2O72-, of which Cr2O72- is dominant; at a high pH of 6-9, there are only species that are predominant: CrO42-[30,31,32].

Effect of Adsorbent Dosage

Figures 6(c) illustrates the investigation of the impact of adsorbent dosage on Cr(VI) in various adsorbent dosages. The adsorbent dosage was changed, ranging from 20g/L to 50g/L while maintaining the other parameters under ideal circumstances. According to the analysis, the percentage of chromium adsorption rose as the dose of the adsorbent increased. The variation in the adsorbent's concentration in the solution and its porous surface area are the primary causes of the rise in adsorbed Cr(VI) with adsorbent dose [33]. As a result, it was discovered that the optimal amounts of adsorbed Cr(VI) on the adsorbent's surface were 4gm/100ml, where the percentages of Cr(VI) and 99.962%, respectively.

Effect of Contact Time

Figures 6(d) demonstrates the investigation of the impact of contact time on the adsorption of Cr (VI). The contact duration is adjusted, ranging from 10 min to 50 min, while maintaining other ideal batch parameters constant. According to the research, the amount of chromium removed rose as the contact time increased. As a result, it was discovered that the optimal amounts of adsorbed Cr(VI) on the adsorbent surface occurred after 50minutes, is 99.962. After that, the adsorption was seen to be steady.

Effect of Temperature

Using other ideal circumstances held constant, the temperature was attuned from 20º to 50ºC (Figure 6(e)) to examine the impact of contact duration on chromium adsorption. The research revealed that as temperature increased, so did the elimination of chromium. By increasing the kinetic energy of the chromium ions, maximum adsorption occurred at 40ºC by the diffusion of Cr(VI) ions to the AC surface. As a result, the frequency of collisions between the Cr(VI) ions and the AC surface rises, leading to an increase in adsorption [32,33]. Because of the low kinetic energy of Cr(VI) species at temperatures below 40ºC, there is less interaction between AC sites and Cr(VI) species, which results in less adsorption. When temperatures rise over 40ºC, the kinetic energy of Cr(VI) species surpasses the attraction potential between AC sites and Cr(VI) species, resulting in inadequate contact between the two groups. Based on the acquired data, we determined that the highest amount of chromium could be removed under optimal conditions of 3pH, 40g/l adsorbent dosage, 50minutes of contact time, and 200rpm swirling speed at 40ºC. As a result, the effluent's chromium content complies with the MoEF & CC, Government of India, and discharge limit for surface water disposal. Here, a greater starting Cr(VI) concentration and a larger adsorbent dose are needed to meet the strict discharge threshold of 0.1 mg/L Cr(VI) (EP Act 1986) [34].

Adsorption Kinetics Study

In order to determine the pace of the adsorption process, various adsorption kinetics are examined and illustrated in Figure 7. The details of the kinetics investigation indicate that the adsorption of Cr(VI) ions follows both the pseudo-first order kinetic model and pseudo-second order kinetics with a coefficient correlation R2 value more than 0.9. However, higher conformance was shown with pseudo first order for Cr(VI) with R2 values of 0.991(Figure7a) followed by pseudo second order for Cr(VI) with R2 0.949(Fig. 7b). This indicates that Cr(VI) is absorbed by chemical adsorption processes, which were predicated on the hypothesis that chemisorptions involving the sharing and exchange of electrons may be the rate-determining step [32].

Figure 7: Pseudo (a) first order and (b) Second order kinetic model on removal of Cr(VI) activated carbon of Zea mays.

Conclusion

The maize cob, botanically known as Zea mays, is a byproduct of a cereal plant that was used to make activated carbon. Sulfuric acid was employed to chemically activate the maize cob, which allowed for the effective chemosorption of Cr(VI) out of waste water containing chromium. The synthesized AC's large surface area and abundance of hydroxyl and carboxyl groups are what give it the ability to absorb Cr(VI). Various analyses were carried out using diverse parameters, including pH, adsorbent dose, contact duration, temperature, and initial concentration. The ideal conditions for adsorption were discovered at pH3, adsorbent dose of 40g/L, contact duration of 50min, temperature of 40ºC, and stirring speed of 200rpm for all three initial chromium concentrations (100mg/L, 200mg/L, and 300mg/L) in surface water bodies. It was discovered that the process was chemosorption and dose-proportional to the adsorbent. Although the first- order model exhibits greater agreement with an R2 value of 0.991, the kinetic modeling data demonstrated that the adsorption was in good agreement with pseudo-first-order and second- order models. Zea mays bio-adsorbent demonstrated both productivity in the adsorption of dangerous heavy metals as Cr(VI) and environmentally beneficial waste management. When it came to the adsorption of Cr(VI) from industrial waste water for routine discharge to inland surface water bodies, activated corncob carbon was thought to be a viable bio-adsorbent.

Acknowledgement

The authors are very much thankful to Department of Chemistry, NIST University, for providing the lab facility and financial support to execute this research work.

Declarations

Conflict of Interest: The authors declare that they have no conflicts of interest with this research project or the publication of the resulting manuscript.

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