Enhanced Adsorption Capacities of Fungicides Using Peanut Shell Biochar via Successive Chemical Modiﬁcation with KMnO 4 and KOH

: This study explored the effects of peanut shell biochar (PSB) on the adsorption capacities of fungicides with and without successive chemical modiﬁcations, using KMnO 4 and KOH (PSB OX-A ), in order to provide a valuable understanding of their adsorption mechanisms and behaviors. To this end, the physicochemical properties of PSB and PSB OX-A were examined by using the Brunauer– Emmett–Teller method, Fourier transform infrared spectroscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer. The effects of temperature, ionic strength, and humic acids on the adsorption of fungicides, using PSB and PSB OX-A , were estimated through batch experiments. Furthermore, adsorption kinetics, isotherms, and thermodynamics were studied. The maximum adsorption capacities of fungicides by PSB OX-A were estimated to be more notable ( Q max of carbendazim = 531.2 µ mol g − 1 , Q max of pyrimethanil = 467.7 µ mol g − 1 , and Q max of tebuconazole = 495.1 µ mol g − 1 ) than PSB ( Q max of carbendazim = 92.6 µ mol g − 1 , Q max of pyrimethanil = 61.7 µ mol g − 1 , and Q max of tebuconazole = 66.7 µ mol g − 1 ). These ﬁndings suggest that successive chemical modiﬁcation using KMnO 4 and KOH could potentially be used to effectively fabricate PSB to remove fungicides in water-treatment processes. the presence of HA (removal efﬁciency without HA: CAR = 95.2 ± 0.02%, PYR = 89.7 ± 0.07%, and TEB = 93.7 ± 0.02%; removal efﬁciency with HA: CAR = 93.8 ± 0.3%, PYR = 88.9 ± 0.3%, and TEB = 93.3 ± 0.07%). These observations suggested that the adsorption behavior of CAR, PYR, and TEB by PSB and PSB OX-A were outcompeted by HA adsorption [12]. m 2 g − 1 ) and total pore volume (0.12 cm 3 g − 1 ). The PSB and PSB OX-A were well ﬁtted with the pseudo-second-order kinetic ( R 2 = 0.999), and the equilibrium adsorption capacities of CAR, PYR, and TEB on PSB OX-A ( Q e,exp = 179.7–196.9 µ mol g − 1 ) were greater than those of PSB ( Q e,exp = 6.1–15.1 µ mol g − 1 ). These ﬁndings indicate that chemisorption plays a crucial role in the adsorption of CAR, PYR, and TEB. Moreover, the Langmuir isotherms predominantly governed the removal of fungicides from the homogeneous surfaces of PSB and PSB OX-A (monolayer adsorption, R 2 = 0.996–0.999). The removal efﬁciencies of CAR, PYR, and TEB using PSB and PSB OX-A gradually increased with increasing temperature and NaCl concentration. Although HA could interfere with CAR, PYR, and TEB adsorptions by PSB and PSB OX-A , the removal efﬁciencies of fungicides by PSB OX-A (88.9–93.8%) were higher when compared to PSB (2.4–6.8%). These results suggest that successive KMnO 4 and KOH modiﬁcation may be a promising option in improving the adsorption capacities of PSB for removing CAR, PYR, and TEB from a real-scale water treatment plant. Future studies need to provide the information for optimum reuse conditions to regenerate the peanut shell biochars with continuous adsorption ability.

Recently, several researchers have recognized that adsorption is the most efficient treatment option; moreover, its operating cost for fungicide removal in water-treatment plants is low [6]. Activated carbon (AC), a representative adsorbent, is commonly utilized

Chemicals
All chemicals and fungicides were of analytical grade. CAR (methyl N-(1H-benzimidazol-2-yl)carbamate), PYR (4,6-dimethyl-N-phenylpyrimidin-2-amine), TEB (1-(4-chlorophenyl)-4,4-dimethyl-3-(1,2,4-triazol-1-ylmethyl)pentan-3-ol), KMnO 4 , KOH, sodium hydroxide (NaOH), hydrochloric acid (HCl), sodium chloride (NaCl), and HA were purchased from Sigma-Aldrich (St. Louis, MO, USA). High-performance liquid chromatography (HPLC)grade acetonitrile (ACN) was obtained from J.T. Baker (Deventer, Netherlands), and phosphoric acid (H 3 PO 4 ) was purchased from FUJIFILM Wako Pure Chemical Corporation (Osaka, Japan). The use of ACN is due to its strong solvation properties for a wide range of polar and nonpolar organic solutes and advantageous properties, including low viscosity and low toxicity [19]. A mixed stock solution containing CAR, PYR, and TEB (concentration of each fungicide = 1 mmol L −1 ) was prepared by using ACN and deionized (DI) water (50:50, v/v). DI water was produced by using a Nanopure Water System (electrical resistivity > 18.2 MΩ cm −1 ; Barnstead, Lake Balboa, CA, USA), and it was used to make the samples. These stock solutions were stored at 4 • C, in the dark, prior to use. The physicochemical properties of CAR, PYR, and TEB are summarized in Table 1.  wide range of polar and nonpolar organic solutes and advantageous properties, including low viscosity and low toxicity [19]. A mixed stock solution containing CAR, PYR, and TEB (concentration of each fungicide = 1 mmol L −1 ) was prepared by using ACN and deionized (DI) water (50:50, v/v). DI water was produced by using a Nanopure Water System (electrical resistivity > 18.2 MΩ cm −1 ; Barnstead, Lake Balboa, CA, USA), and it was used to make the samples. These stock solutions were stored at 4 °C, in the dark, prior to use. The physicochemical properties of CAR, PYR, and TEB are summarized in Table 1.

Preparation of PSB and PSBOX-A
The detailed preparation method of the PSB via successive chemical modification with KMnO4 and KOH was modified in a previous study [20].

PSB
Peanut shells were purchased from a local grocery store in Chuncheon-si (Gangwondo, Korea). They were rinsed several times with DI water and dried in an oven for 24 h, at 105 °C. The PSB was pyrolyzed by using a tubular furnace (PyroTech, Namyangju-si, Korea) for 2 h, at 700 °C, under N2 atmosphere (heating rate = 10 °C min −1 ; the N2 flow rate = 0.25 L min −1 ). After the entire procedure was completed, the produced PSB was rinsed with DI water and dried in an oven at 105 °C, for 12 h.

PSBOX-A
To enhance the surface functionality of PSB, the PSB (5 g) produced was mixed with 0.5% KMnO4 (10 mL) by stirring at 20 ± 0.5 °C for 4 h and drying in an oven, at 60 °C, for 4 h. The modified PSB with KMnO4 was pyrolyzed by using a tubular furnace at 700 °C, for 2 h, under N2 atmosphere (heating rate = 10 °C min −1 ; N2 flow rate = 0.25 L min −1 ). The modified PSB with KMnO4 was rinsed with DI water several times and dried in an oven, at 105 °C, for 12 h. Furthermore, the modified PSB with KMnO4 was added to KOH (15 g) and pyrolyzed in a tubular furnace, at 700 °C (heating rate = 10 °C min −1 ), for 1 h, under N2 atmosphere (flow rate = 0.25 L min −1 ). The PSBOX-A produced was rinsed with DI water several times and dried in an oven, at 60 °C, for 24 h. The dried PSBOX-A was passed through a 100-mesh sieve, to maintain a uniform size, after which it was stored in a desiccator prior to analysis. wide range of polar and nonpolar organic solutes and advantageous properties, including low viscosity and low toxicity [19]. A mixed stock solution containing CAR, PYR, and TEB (concentration of each fungicide = 1 mmol L −1 ) was prepared by using ACN and deionized (DI) water (50:50, v/v). DI water was produced by using a Nanopure Water System (electrical resistivity > 18.2 MΩ cm −1 ; Barnstead, Lake Balboa, CA, USA), and it was used to make the samples. These stock solutions were stored at 4 °C, in the dark, prior to use. The physicochemical properties of CAR, PYR, and TEB are summarized in Table 1.

Preparation of PSB and PSBOX-A
The detailed preparation method of the PSB via successive chemical modification with KMnO4 and KOH was modified in a previous study [20].

PSB
Peanut shells were purchased from a local grocery store in Chuncheon-si (Gangwondo, Korea). They were rinsed several times with DI water and dried in an oven for 24 h, at 105 °C. The PSB was pyrolyzed by using a tubular furnace (PyroTech, Namyangju-si, Korea) for 2 h, at 700 °C, under N2 atmosphere (heating rate = 10 °C min −1 ; the N2 flow rate = 0.25 L min −1 ). After the entire procedure was completed, the produced PSB was rinsed with DI water and dried in an oven at 105 °C, for 12 h.

PSBOX-A
To enhance the surface functionality of PSB, the PSB (5 g) produced was mixed with 0.5% KMnO4 (10 mL) by stirring at 20 ± 0.5 °C for 4 h and drying in an oven, at 60 °C, for 4 h. The modified PSB with KMnO4 was pyrolyzed by using a tubular furnace at 700 °C, for 2 h, under N2 atmosphere (heating rate = 10 °C min −1 ; N2 flow rate = 0.25 L min −1 ). The modified PSB with KMnO4 was rinsed with DI water several times and dried in an oven, at 105 °C, for 12 h. Furthermore, the modified PSB with KMnO4 was added to KOH (15 g) and pyrolyzed in a tubular furnace, at 700 °C (heating rate = 10 °C min −1 ), for 1 h, under N2 atmosphere (flow rate = 0.25 L min −1 ). The PSBOX-A produced was rinsed with DI water several times and dried in an oven, at 60 °C, for 24 h. The dried PSBOX-A was passed through a 100-mesh sieve, to maintain a uniform size, after which it was stored in a desiccator prior to analysis. wide range of polar and nonpolar organic solutes and advantageous properties, including low viscosity and low toxicity [19]. A mixed stock solution containing CAR, PYR, and TEB (concentration of each fungicide = 1 mmol L −1 ) was prepared by using ACN and deionized (DI) water (50:50, v/v). DI water was produced by using a Nanopure Water System (electrical resistivity > 18.2 MΩ cm −1 ; Barnstead, Lake Balboa, CA, USA), and it was used to make the samples. These stock solutions were stored at 4 °C, in the dark, prior to use. The physicochemical properties of CAR, PYR, and TEB are summarized in Table 1.

Preparation of PSB and PSBOX-A
The detailed preparation method of the PSB via successive chemical modification with KMnO4 and KOH was modified in a previous study [20].

PSB
Peanut shells were purchased from a local grocery store in Chuncheon-si (Gangwondo, Korea). They were rinsed several times with DI water and dried in an oven for 24 h, at 105 °C. The PSB was pyrolyzed by using a tubular furnace (PyroTech, Namyangju-si, Korea) for 2 h, at 700 °C, under N2 atmosphere (heating rate = 10 °C min −1 ; the N2 flow rate = 0.25 L min −1 ). After the entire procedure was completed, the produced PSB was rinsed with DI water and dried in an oven at 105 °C, for 12 h.

PSBOX-A
To enhance the surface functionality of PSB, the PSB (5 g) produced was mixed with 0.5% KMnO4 (10 mL) by stirring at 20 ± 0.5 °C for 4 h and drying in an oven, at 60 °C, for 4 h. The modified PSB with KMnO4 was pyrolyzed by using a tubular furnace at 700 °C, for 2 h, under N2 atmosphere (heating rate = 10 °C min −1 ; N2 flow rate = 0.25 L min −1 ). The modified PSB with KMnO4 was rinsed with DI water several times and dried in an oven, at 105 °C, for 12 h. Furthermore, the modified PSB with KMnO4 was added to KOH (15 g) and pyrolyzed in a tubular furnace, at 700 °C (heating rate = 10 °C min −1 ), for 1 h, under N2 atmosphere (flow rate = 0.25 L min −1 ). The PSBOX-A produced was rinsed with DI water several times and dried in an oven, at 60 °C, for 24 h. The dried PSBOX-A was passed through a 100-mesh sieve, to maintain a uniform size, after which it was stored in a desiccator prior to analysis.

Preparation of PSB and PSB OX-A
The detailed preparation method of the PSB via successive chemical modification with KMnO 4 and KOH was modified in a previous study [20].

PSB
Peanut shells were purchased from a local grocery store in Chuncheon-si (Gangwondo, Korea). They were rinsed several times with DI water and dried in an oven for 24 h, at 105 • C. The PSB was pyrolyzed by using a tubular furnace (PyroTech, Namyangju-si, Korea) for 2 h, at 700 • C, under N 2 atmosphere (heating rate = 10 • C min −1 ; the N 2 flow rate = 0.25 L min −1 ). After the entire procedure was completed, the produced PSB was rinsed with DI water and dried in an oven at 105 • C, for 12 h.

PSB OX-A
To enhance the surface functionality of PSB, the PSB (5 g) produced was mixed with 0.5% KMnO 4 (10 mL) by stirring at 20 ± 0.5 • C for 4 h and drying in an oven, at 60 • C, for 4 h. The modified PSB with KMnO 4 was pyrolyzed by using a tubular furnace at 700 • C, for 2 h, under N 2 atmosphere (heating rate = 10 • C min −1 ; N 2 flow rate = 0.25 L min −1 ). The modified PSB with KMnO 4 was rinsed with DI water several times and dried in an oven, at 105 • C, for 12 h. Furthermore, the modified PSB with KMnO 4 was added to KOH (15 g) and pyrolyzed in a tubular furnace, at 700 • C (heating rate = 10 • C min −1 ), for 1 h, under N 2 atmosphere (flow rate = 0.25 L min −1 ). The PSB OX-A produced was rinsed with DI water several times and dried in an oven, at 60 • C, for 24 h. The dried PSB OX-A was passed through a 100-mesh sieve, to maintain a uniform size, after which it was stored in a desiccator prior to analysis.

. Specific Surface Area and Porosity
The specific surface areas (m 2 g −1 ) of PSB and PSB OX-A were determined by using the Brunauer-Emmett-Teller (BET) method on the N 2 adsorption-desorption isotherms at 77.3 K in the relative pressure range of 0.01-0.99 (ASAP 2020 Plus, Micromeritics, GA, USA). The total pore volume (cm 3 g −1 ) and average pore size (nm) were calculated by using the Barrett-Joyner-Halenda (BJH) method [21].

Elemental Compositions
The elemental compositions (i.e., carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S)) of PSB and PSB OX-A were measured by using a EuroEA3000 elemental analyzer (EuroVector S.p.A, Via F.lli Cuzio, Italy). Ash content was calculated by subtracting the C, H, O, N, and S contents from the total amount of PSB and PSB OX-A . The atomic molar ratios of H/C and O/C + N/C were used to reveal the aromaticity and polarity of PSB and PSB OX-A , respectively [21].

Scanning Electron Microscopy Analysis
The surface morphologies of PSB and PSB OX-A were identified by using an S-4800 scanning electron microscope (SEM; Hitachi, Tokyo, Japan) with an energy dispersive X-ray (EDX) spectrometer.

Fourier Transform Infrared Spectroscopy Analysis
Fourier transform infrared (FTIR) spectroscopy with a KBr pellet was used to qualitatively analyze the surface functional groups of PSB and PSB OX-A ranging between 400 and 4000 cm −1 (Vertex 70, Bruker, Billerica, MA, USA).

Analytical Methods
The concentrations of CAR, PYR, and TEB in the samples were measured by using HPLC coupled with a column (XDB C18; ZORBAX Eclipse ® , 4.6 mm × 150 mm, inner diameter = 5 µm; Agilent, Santa Clara, CA, USA) and a UVA detector (SPD-10AVP, Shimadzu, Kyoto, Japan) at 210 nm. The mobile phase (CAN: 0.05 M H 3 PO 4 (50:50, v/v)) was operated under isocratic conditions (flow rate = 1.0 mL min −1 ) for 15 min. Various sample conditions were used to evaluate the effects of temperature, ionic strength, and HA on the adsorption of CAR, PYR, and TEB when using PSB and PSB OX-A (the concentration of each fungicide = 10 µmol L −1 , temperature = 15-35 • C, concentrations of NaCl = 0-0.1 M, and concentration of HA = 5 mg L −1 ). All adsorption experiments were conducted in triplicate, using a shaking incubator (Vision Scientific, Daejeon, Korea). Then, the sample solutions were filtered by using a nominal pore size of 0.7 µm glass fiber filter (GF/F; Whatman, Maidstone, UK) to eliminate PSB and PSB OX-A .
The amounts of CAR, PYR, and TEB adsorbed per unit mass of PSB and PSB OX-A at equilibrium, Q e (µmol g −1 ), and removal efficiencies (%) of CAR, PYR, and TEM by PSB and PSB OX-A were calculated by using the following equations: where C 0 and C e (µmol L −1 ) are the initial and equilibrium concentrations of CAR, PYR, and TEB, respectively. V (L) is the sample solution volume, and M (g) is the amount of PSB and PSB OX-A . The adsorption kinetics of CAR, PYR, and TEB were examined by using the pseudofirst-order (Equation (3)) and pseudo-second-order (Equation (4)) kinetic models (adsorbent dosage = 50 mg L −1 , initial concentration of each fungicide = 10 µmol L −1 , contact time = 0-24 h, agitation speed = 150 rpm, temperature = 25 • C, and pH = 7.0) [22]: where Q t (µmol g −1 ) is the amount of adsorbed CAR, PYR, and TEB on PSB and PSB OX-A at adsorption time t (h). Moreover, k 1 (1/h) and k 2 (g µmol −1 ·h) are the rate constants of the pseudo-first-order and pseudo-second-order models, respectively. The adsorption isotherms of CAR, PYR, and TEB were investigated at five different initial concentrations (10,20,30,40, and 50 µmol L −1 ), under fixed conditions (adsorbent dosage = 50 mg L −1 , contact time = 24 h, agitation speed = 150 rpm, temperature = 25 • C, and pH = 7.0) [23].
Freundlich isotherm : where Q max (µmol g −1 ) is the maximum adsorption capacity in the Langmuir isotherm model, and K L (L µmol −1 ) is the equilibrium constant of the linearized Langmuir isotherm model. R L = 1/(1 + K L C 0 ), derived from K L , is used to compare the adsorption affinity of the Langmuir isotherms. K F (µmol 1−1/n L 1/n g −1 ) and n (dimensionless) are constants associated with the relative maximum adsorption capacity and adsorption intensity, respectively [24]. The thermodynamic parameters of CAR, PYR, and TEB adsorption were estimated by using Equations (7)-(9) [25].
where K d (L g −1 ) is the partition coefficient; ∆G • in (kJ mol −1 ), ∆H • in (kJ mol −1 ), and ∆S • (J mol −1 ·K) are the Gibbs free energy, enthalpy, and entropy, respectively. R (J mol −1 ·K) and T (K) are the ideal gas constant (8.314 J mol −1 ·K) and the absolute temperature of the sample solutions. ∆H • and ∆S • were calculated as the slope and intercept in the linear graph of ln(K d ) and 1/T, respectively.

Physicochemical Properties of PSB and PSB OX-A
The physicochemical properties (e.g., bulk element and ash contents, the atomic molar ratio, specific surface area, total pore volume, average pore size, and BET isotherms) associated with the adsorption capacity of PSB and PSB OX-A are presented in Figure 1 and Table 2. The bulk element and ash contents of PSB (C = 86.6%, H = 1.6%, O = 3.7%, N = 1.7%, S = 0.1%, and ash = 6.3%) and PSB OX-A (C = 82.1%, H = 1.1%, O = 4.9%, N = 1.3%, S = 0.2%, and ash = 10.5%) have revealed considerable differences due to the successive KMnO 4 and KOH modification processes. Furthermore, PSB OX-A presented lower atomic molar ratios of H/C (0.16) than that of PSB (0.23), but the sum of O/C and N/C values for PSB OX-A (0.05) were similar to those of PSB (0.05). These findings indicate that PSB OX-A has a higher aromaticity (H/C value: PSB > PSB OX-A ) than PSB [26]. Additionally, PSB OX-A had a higher specific surface area and total pore volume than that of PSB, but the average pore size of PSB OX-A was smaller than that of PSB. The specific surface area (1977.6 m 2 g −1 ) and total pore volume (0.12 cm 3 g −1 ) of PSB OX-A were significantly greater than those of PSB (specific surface area = 93.9 m 2 g −1 and total pore volume = 0.04 cm 3 g −1 ), given that the porous structures were changed by the successive chemical modification using KMnO 4 and KOH [11]. However, the average pore size of PSB OX-A (3.4 nm) was not significantly different from that of PSB (3.8 nm). Therefore, the CAR, PYR, and TEB adsorption capacities of PSB OX-A were expected to be enhanced compared with those of PSB. total pore volume (0.12 cm 3 g −1 ) of PSBOX-A were significantly greater than those of PSB (specific surface area = 93.9 m 2 g −1 and total pore volume = 0.04 cm 3 g −1 ), given that the porous structures were changed by the successive chemical modification using KMnO4 and KOH [11]. However, the average pore size of PSBOX-A (3.4 nm) was not significantly different from that of PSB (3.8 nm). Therefore, the CAR, PYR, and TEB adsorption capacities of PSBOX-A were expected to be enhanced compared with those of PSB.  The SEM images of PSB and PSBOX-A are shown in Figure 2. The surface of PSB is smooth and flat, but PSBOX-A has porous and uneven structures. These results indicate that chemical modification using KMnO4 and KOH might change the surface morphology of the PSB with respect to the adsorption of fungicides [27].  The SEM images of PSB and PSB OX-A are shown in Figure 2. The surface of PSB is smooth and flat, but PSB OX-A has porous and uneven structures. These results indicate that chemical modification using KMnO 4 and KOH might change the surface morphology of the PSB with respect to the adsorption of fungicides [27]. cates the O-H groups of alcohols [14]. The IR peaks at 1570 and 1180 cm −1 could be attributed to the vibrations of the C=C stretching of aromatic groups and the C-O stretching of phenolic and carboxylic groups, respectively [28,29]. The intensities of the IR peaks (i.e., OH alcohol groups, C=C aromatic groups, and C-O phenolic and carboxylic groups) for PSBOX-A were significantly higher than those of PSB. These observations suggest that the differences in the adsorption capacities of PSB and PSBOX-A could influence the adsorption of fungicides because of the successive chemical modifications with KMnO4 and KOH.

Effects of Absorbent Dosages
The effects of PSB and PSBOX-A dosages on the removal efficiencies of CAR, PYR, and TEB are shown in Figure 4. The adsorption capacities of CAR, PYR, and TEB using PSB and PSBOX-A continuously decreased, and the removal efficiency of fungicides on PSB and PSBOX-A gradually increased. This is because, when the initial concentrations of CAR, PYR, and TEB are fixed, the adsorption capacity per unit of the adsorbents tends to decline as   [14]. The IR peaks at 1570 and 1180 cm −1 could be attributed to the vibrations of the C=C stretching of aromatic groups and the C-O stretching of phenolic and carboxylic groups, respectively [28,29]. The intensities of the IR peaks (i.e., OH alcohol groups, C=C aromatic groups, and C-O phenolic and carboxylic groups) for PSB OX-A were significantly higher than those of PSB. These observations suggest that the differences in the adsorption capacities of PSB and PSB OX-A could influence the adsorption of fungicides because of the successive chemical modifications with KMnO 4 and KOH.  Figure 3 shows the FTIR spectra of PSB and PSBOX-A. The IR peak at 3420 cm −1 indicates the O-H groups of alcohols [14]. The IR peaks at 1570 and 1180 cm −1 could be attributed to the vibrations of the C=C stretching of aromatic groups and the C-O stretching of phenolic and carboxylic groups, respectively [28,29]. The intensities of the IR peaks (i.e., OH alcohol groups, C=C aromatic groups, and C-O phenolic and carboxylic groups) for PSBOX-A were significantly higher than those of PSB. These observations suggest that the differences in the adsorption capacities of PSB and PSBOX-A could influence the adsorption of fungicides because of the successive chemical modifications with KMnO4 and KOH.

Effects of Absorbent Dosages
The effects of PSB and PSBOX-A dosages on the removal efficiencies of CAR, PYR, and TEB are shown in Figure 4. The adsorption capacities of CAR, PYR, and TEB using PSB and PSBOX-A continuously decreased, and the removal efficiency of fungicides on PSB and PSBOX-A gradually increased. This is because, when the initial concentrations of CAR, PYR, and TEB are fixed, the adsorption capacity per unit of the adsorbents tends to decline as

Effects of Absorbent Dosages
The effects of PSB and PSB OX-A dosages on the removal efficiencies of CAR, PYR, and TEB are shown in Figure 4. The adsorption capacities of CAR, PYR, and TEB using PSB and PSB OX-A continuously decreased, and the removal efficiency of fungicides on PSB and PSB OX-A gradually increased. This is because, when the initial concentrations of CAR, PYR, and TEB are fixed, the adsorption capacity per unit of the adsorbents tends to decline as the amount of PSB and PSB OX-A increases. Similar behavior was previously observed during the removal of the fungicides (e.g., triclosan and triclocarban) using Zr-based magnetic metal-organic frameworks [30]. Based on these experiments on the removal efficiency of the amount of PSB and PSBOX-A increases. Similar behavior was previously observed during the removal of the fungicides (e.g., triclosan and triclocarban) using Zr-based magnetic metal-organic frameworks [30]. Based on these experiments on the removal efficiency of CAR, PYR, and TEB according to the PSB and PSBOX-A dosages, 50 mg L −1 was selected as the optimal dosage and applied to the subsequent experiments.
(a) (b)  Figure 5 shows the adsorption kinetics of CAR, PYR, and TEB when using PSB and PSBOX-A. The fast adsorption reaction was completed within 4 h for fungicides on the PSB and PSBOX-A surfaces. After 4 h, the removal efficiencies of CAR, PYR, and TEB were increased by PSB and PSBOX-A because the activated binding sites on PSB and PSBOX-A surfaces were saturated [12]. The removal efficiencies of CAR, PYR, and TEB by PSB (removal efficiency of CAR = 7.3 ± 0.04%, removal efficiency of PYR = 3.1 ± 0.04%, and removal efficiency of TEB = 5.8 ± 0.08%) were considerably lower than those of CAR, PYR, and TEB by PSBOX-A (removal efficiency of CAR = 95.1 ± 0.1%, removal efficiency of PYR = 89.9 ± 0.02%, and removal efficiency of TEB = 92.7 ± 0.1%). These observations were attributed to the differences in the physicochemical properties (i.e., specific surface area, total pore volume, and surface functional groups) of PSB and PSBOX-A. Table 3 presents the adsorption kinetics for CAR, PYR, and TEB when using PSB and PSBOX-A. The pseudo-second-order model (R 2 = 0.999) might better explain the adsorption of fungicides when using PSB and PSBOX-A than the pseudo-first-order model (R 2 = 0.882-0.985). The equilibrium adsorption capacities of the fungicides (Qe,exp) on those of PSB (Qe,exp of the PSBOX-A = 179.7-196.9 μmol g −1 ) were much greater than those of PSB (Qe,exp of the PSB = 6.1-15.1 μmol g −1 ). Furthermore, the Qe,exp values of CAR, PYR, and TEB toward the PSB and PSBOX-A demonstrate similar trends as those of the theoretical adsorption capacities (Qe, cal) calculated by the pseudo-second-order model (Qe, cal of the PSB = 6.7-15.4 μmol g −1 , Qe, cal of the PSBOX-A = 184.9-202.0 μmol g −1 ). These results suggested that the adsorption of CAR, PYR, and TEB on PSB and PSBOX-A might be chemisorption [31].  Figure 5 shows the adsorption kinetics of CAR, PYR, and TEB when using PSB and PSB OX-A . The fast adsorption reaction was completed within 4 h for fungicides on the PSB and PSB OX-A surfaces. After 4 h, the removal efficiencies of CAR, PYR, and TEB were increased by PSB and PSB OX-A because the activated binding sites on PSB and PSB OX-A surfaces were saturated [12]. The removal efficiencies of CAR, PYR, and TEB by PSB (removal efficiency of CAR = 7.3 ± 0.04%, removal efficiency of PYR = 3.1 ± 0.04%, and removal efficiency of TEB = 5.8 ± 0.08%) were considerably lower than those of CAR, PYR, and TEB by PSB OX-A (removal efficiency of CAR = 95.1 ± 0.1%, removal efficiency of PYR = 89.9 ± 0.02%, and removal efficiency of TEB = 92.7 ± 0.1%). These observations were attributed to the differences in the physicochemical properties (i.e., specific surface area, total pore volume, and surface functional groups) of PSB and PSB OX-A .

Pseudo-Fist-Order
Pseudo-Second-Order Qe,cal Removal efficiency (%)  Table 3 presents the adsorption kinetics for CAR, PYR, and TEB when using PSB and PSB OX-A . The pseudo-second-order model (R 2 = 0.999) might better explain the adsorption of fungicides when using PSB and PSB OX-A than the pseudo-first-order model (R 2 = 0.882-0.985). The equilibrium adsorption capacities of the fungicides (Q e,exp ) on those of PSB (Q e,exp of the PSB OX-A = 179.7-196.9 µmol g −1 ) were much greater than those of PSB (Q e,exp of the PSB = 6.1-15.1 µmol g −1 ). Furthermore, the Q e,exp values of CAR, PYR, and TEB toward the PSB and PSB OX-A demonstrate similar trends as those of the theoretical adsorption capacities (Q e, cal ) calculated by the pseudo-second-order model (Q e, cal of the PSB = 6.7-15.4 µmol g −1 , Q e, cal of the PSB OX-A = 184.9-202.0 µmol g −1 ). These results suggested that the adsorption of CAR, PYR, and TEB on PSB and PSB OX-A might be chemisorption [31].

Adsorption Isotherms of Fungicides
The adsorption of CAR, PYR, and TEB by PSB and PSB OX-A were examined by using the Langmuir and Freundlich isotherm models ( Figure 6 and Table 4). The adsorption behaviors of CAR, PYR, and TEB with respect to PSB and PSB OX-A are better explained by the Langmuir isotherm model (R 2 = 0.996-0.999) than the Freundlich isotherm model (R 2 = 0.764-0.995). This indicated that monolayer adsorption played a key role in removing the fungicides from the homogeneous surfaces of PSB and PSB OX-A [32]. The adsorption affinities of CAR, PYR, and TEB to PSB and PSB OX-A were evaluated by using the R L values. The R L values, namely (i) R L > 1: unfavorable, (ii) R L = 1: linear, (iii) 0 < R L < 1: favorable, and (iv) R L = 0: irreversible, of the Langmuir isotherm model were used to identify the maximum adsorption capacities of CAR, PYR, and TEB by using PSB and PSB OX-A [33]. The R L values of PSB and PSB OX-A were estimated to be favorable (R L = 0.08-0.8).  Table 4. Isotherm parameters for the adsorptions of fungicides using PSB and PSB OX-A (agitation speed = 150 rpm; contact time = 24 h; absorbent dosage = 50 mg L −1 ; initial concentration of each fungicide = 10 µM; temperature = 25 • C; pH = 7.0).

Absorbents Compounds
Langmuir Freundlich  Figure 7 depicts the adsorption behaviors of CAR, PYR, and TEB for PSB and PSB OX-A at three different pH values (pH = 3, 7, and 11). The removal efficiencies of CAR (11.5% → 6.9%), PYR (4.8% → 2.7%), and TEB (5.6% → 3.1%) by the PSB were negative affected by the increase of pH values. However, the removal efficiencies of CAR (97.0% → 96.6%) and PYR (91.0% → 90.6%) by the PSB OX-A were not significantly different under the different pH values. The change in pH values strongly influenced the removal efficiency of TEB (94.3% → 93.2%) by the PSB OX-A due to the lower pKa value of TEB (pK a = 2.01) compared with the CAR (pK a = 4.28) and PYR (pK a = 3.44). Moreover, the deprotonated fungicides could promote the electrostatic repulsive interaction between the fungicides and the PSB under the pH value was higher than their pK a values [12]. These observations could explain that the electrostatic interactions between fungicides and absorbents under the different pH values played a key role in the adsorptions of the CAR, PYR, and TEB using the PSB and PSB OX-A .

Conclusions
This study examined the effects of successive KMnO4 and KOH modifications on the physicochemical properties of PSB associated with the adsorption behaviors of CAR, PYR, and TEB. Compared to PSB, PSBOX-A presented a higher specific surface area (1977.6 m 2 g −1 ) and total pore volume (0.12 cm 3 g −1 ). The PSB and PSBOX-A were well fitted with the pseudo-second-order kinetic (R 2 = 0.999), and the equilibrium adsorption capacities of CAR, PYR, and TEB on PSBOX-A (Qe,exp = 179.7-196.9 μmol g −1 ) were greater than those of PSB (Qe,exp = 6.1-15.1 μmol g −1 ). These findings indicate that chemisorption plays a crucial The effects of HA on the adsorption of CAR, PYR, and TEB for PSB and PSB OX-A are presented in Figure 10. HA, macromolecular compounds with many reactive functional groups, might scavenge the binding sites generated on PSB and PSB OX-A . Thus, HA used in the batch experiments could affect the adsorption affinity of fungicides with adsorbents [38]. The removal efficiencies of CAR, PYR, and TEB by PSB are similar to the existence of HA (removal efficiency without HA: CAR = 7.1 ± 0.07%, PYR = 2.8 ± 0.09%, and TEB = 4.3 ± 0.3%; removal efficiency with HA: CAR = 6.8 ± 0.3%, PYR = 2.4 ± 0.2%, and TEB = 2.8 ± 0.1%). The removal efficiencies of CAR, PYR, and TEB using PSB OX-A are not significantly affected by the presence of HA (removal efficiency without HA: CAR = 95.2 ± 0.02%, PYR = 89.7 ± 0.07%, and TEB = 93.7 ± 0.02%; removal efficiency with HA: CAR = 93.8 ± 0.3%, PYR = 88.9 ± 0.3%, and TEB = 93.3 ± 0.07%). These observations suggested that the adsorption behavior of CAR, PYR, and TEB by PSB and PSB OX-A were outcompeted by HA adsorption [12].

Conclusions
This study examined the effects of successive KMnO4 and KOH modifications on the physicochemical properties of PSB associated with the adsorption behaviors of CAR, PYR, and TEB. Compared to PSB, PSBOX-A presented a higher specific surface area (1977.6 m 2 g −1 ) and total pore volume (0.12 cm 3 g −1 ). The PSB and PSBOX-A were well fitted with the pseudo-second-order kinetic (R 2 = 0.999), and the equilibrium adsorption capacities of CAR, PYR, and TEB on PSBOX-A (Qe,exp = 179.7-196.9 μmol g −1 ) were greater than those of PSB (Qe,exp = 6.1-15.1 μmol g −1 ). These findings indicate that chemisorption plays a crucial role in the adsorption of CAR, PYR, and TEB. Moreover, the Langmuir isotherms predominantly governed the removal of fungicides from the homogeneous surfaces of PSB and PSBOX-A (monolayer adsorption, R 2 = 0.996-0.999). The removal efficiencies of CAR, PYR, and TEB using PSB and PSBOX-A gradually increased with increasing temperature and NaCl concentration. Although HA could interfere with CAR, PYR, and TEB adsorptions by PSB and PSBOX-A, the removal efficiencies of fungicides by PSBOX-A (88.9-93.8%) were higher when compared to PSB (2.4-6.8%). These results suggest that successive KMnO4

Conclusions
This study examined the effects of successive KMnO 4 and KOH modifications on the physicochemical properties of PSB associated with the adsorption behaviors of CAR, PYR, and TEB. Compared to PSB, PSB OX-A presented a higher specific surface area (1977.6 m 2 g −1 ) and total pore volume (0.12 cm 3 g −1 ). The PSB and PSB OX-A were well fitted with the pseudo-second-order kinetic (R 2 = 0.999), and the equilibrium adsorption capacities of CAR, PYR, and TEB on PSB OX-A (Q e,exp = 179.7-196.9 µmol g −1 ) were greater than those of PSB (Q e,exp = 6.1-15.1 µmol g −1 ). These findings indicate that chemisorption plays a crucial role in the adsorption of CAR, PYR, and TEB. Moreover, the Langmuir isotherms predominantly governed the removal of fungicides from the homogeneous surfaces of PSB and PSB OX-A (monolayer adsorption, R 2 = 0.996-0.999). The removal efficiencies of CAR, PYR, and TEB using PSB and PSB OX-A gradually increased with increasing temperature and NaCl concentration. Although HA could interfere with CAR, PYR, and TEB adsorptions by PSB and PSB OX-A , the removal efficiencies of fungicides by PSB OX-A (88.9-93.8%) were higher when compared to PSB (2.4-6.8%). These results suggest that successive KMnO 4 and KOH modification may be a promising option in improving the adsorption capacities of PSB for removing CAR, PYR, and TEB from a real-scale water treatment plant. Future studies need to provide the information for optimum reuse conditions to regenerate the peanut shell biochars with continuous adsorption ability.

Conflicts of Interest:
The authors declare no conflict of interest.