In this study, a porous biochar material derived from waste crab shell was prepared by one-step hydrothermal carbonization and acetic acid activation method at 180°C, which was characterized by SEM, BET, XRD and FTIR. The results show that the as-prepared crab shell biochar (CSB) exhibits a fluffy irregular layered structure with abundant pores and oxygen-containing functional groups, which can facilitate the adsorption of diesel using CSB. In addition, batch adsorption experiments had been performed, effects of initial diesel concentration, adsorption time, adsorbent dosage and pH on the diesel adsorption using CSB were analyzed, which could be observed that CSB has high removal efficiency for diesel, and the maximum removal rate is up to 80.1%. The adsorption isotherms and kinetic studies were also investigated to determine the adsorption mechanism of diesel using CSB, the results show that the Langmuir model and the pseudo-second-order model are more suitable for describing the adsorption of diesel using CSB, indicating that the adsorption of diesel oil by CSB is monolayer chemical adsorption. This study will provide a theoretical basis for the high-value utilization of waste crab shell, which has a great potential in the treatment of oil spill.
Petroleum, known as the blood of industry, is indispensable to the survival and development of all countries in the world. With the acceleration of industrialization, global petroleum consumption has risen sharply over the last decades, which has reached 4.66 billion metric tons in 2018 [
To date, a variety of technologies available for the removal of oil pollution have been developed, such as physical method [
Commonly used biochar preparation methods include high-temperature cracking (also known as oxygen-limited carbonization) and hydrothermal carbonization [
However, to the best of our knowledge, there are few reports on the preparation of crab shell biochar by hydrothermal carbonization using acetic acid as an activator. In this study, a porous biochar derived from waste crab shell was prepared by one-step hydrothermal carbonization and activation method at low temperature using acetic acid as activation reagent. CSB was characterized by SEM, BET, XRD and FTIR. The adsorption properties of as-prepared biochar for diesel oil were investigated by simulating the environment of diesel wastewater. The batch adsorption experiments of diesel were performed using as-prepared absorbent, and the adsorption isotherms and kinetics were also investigated.
Crab shell used in this experiment was obtained from the local market in Zhoushan, China, which was washed with deionized water for several times and dried at 80°C for 2 h. Then the dried crab shell was crushed into powder and used in subsequent pyrolysis experiments. Hydrochloric acid (HCl), sodium hydroxide (NaOH) and acetic acid (CH3COOH) were purchased from Shanghai National Pharmaceutical Chemical Reagent Co., Ltd., China. The chemicals used in this study are analytical and used at reception without further purification.
The pre-treated crab shell powder was soaked in 6% HCl for 4 h at 30°C for decalcification, and then soaked in 6% NaOH for 2 h at 90°C for deproteinization. After being soaked in 50% NaOH for 9 h, the crab shell powder was washed with deionized water for several times until neutral (pH = 7), and then dried in the oven (SENXIN-DGG9030BD, Shanghai, China) at 80°C for 10 h. The pretreated crab shell powder mixed was with 50% acetic acid (crab shell/acetic acid (w/v) = 1:1), then the mixture was carbonized at 180°C for 10 h in the oven. After cooling to room temperature, the prepared crab shell biochar was rinsed using deionized water until neutral, dried in the in the oven at 80°C for 12 h, ground and sieved with 100 mesh, which was denoted as CSB. And in the control group, the pretreated crab shell powder in “
Surface microstructure and morphology of as-prepared sample were investigated by using scanning electron microscopy (SEM, Hitachi S-4800, Tokyo, Japan) at 5.0 KV. N2 adsorption/desorption isotherm was performed on a static volumetric adsorption analyzer (Micromeritics ASAP 2010, Shanghai, China) and calculated with the method of BET. Meanwhile, X-ray diffraction (XRD) patterns of sample were recorded on an Ultima IV X-ray Diffractometer (Ultima IV, Rigaku Corporation, Tokyo, Japan) in the range of 2θ from 10° to 60°. Moreover, the surface functional groups were analyzed by Fourier transform infrared spectra (FTIR, Nicolet 5700, Thermo Corp., USA).
The standard curve is a curve used to describe the quantitative relationship between the concentration (or content) of the substance to be measured and the response signal values of the analytical instrument. Using the diesel standard solution to draw the diesel standard curve, the corresponding concentration value can be found on the standard curve through the measured absorbance value.
0.3 g diesel was mixed with 5 mL petroleum ether in a 100 mL volumetric flask, diluted with petroleum ether to 100 mL, as the diesel standard solution. Take 0 mL, 5 mL, 10 mL, 15 mL, 20 mL and 25 mL diesel standard solution, respectively, and the constant volume was made up to 25 mL with petroleum ether. The absorbance value was measured with petroleum ether as reference at a wavelength of 256 nm by UV-vis spectrophotometer (Model No. UV 2600, Shimadzu, Shanghai, China), and the diesel standard curve was drawn as shown in
The as-prepared absorbent was added into 100 mL diesel wastewater for adsorption experiments. The effects of diesel initial concentration, reaction time, initial pH and absorbent dosage on the diesel adsorption were also investigated as shown in
where, the adsorption rate of diesel at equilibrium is denoted as R (%), the adsorption capacity of diesel at equilibrium is denoted as qe, the initial and equilibrium concentrations of diesel wastewater are denoted as C0 and Ce, respectively, and the dosage of CSB and the volume of diesel wastewater solution are denoted as m(g) and V(L), respectively.
Conditions | Diesel initial concentration (mg/L) | Adsorption time (h) | Adsorption pH | Absorbent dosage (g) |
---|---|---|---|---|
1 | 100 | 0.5 | 5 | 0.05 |
2 | 200 | 1 | 6 | 0.10 |
3 | 300 | 2 | 7 | 0.15 |
4 | 400 | 3 | 8 | 0.20 |
5 | 500 | 4 | 9 | 0.25 |
6 | 600 | 6 |
0.1 g CSB absorbent was added into 100 mL diesel wastewater with different initial concentrations, respectively, and the adsorption process was carried out for 5 h. The Langmuir and Freundlich adsorption isotherms were used to analyze the equilibrium performance, as follows:
where the equilibrium concentration of diesel fuel is denoted as Ce (mg/L). The adsorption capacity of diesel fuel at equilibrium is denoted as qe (mg/g), and the saturation adsorption capacity is denoted as qm (mg/g). The Langmuir adsorption equilibrium constant is denoted by KL (L/mg) and the Freundlich constant is denoted by KF [(mg/g)(L/mg)1/n], 1/n representing the energy partition depending on the adsorption properties and adsorbent energy.
0.1 g CSB adsorbent was added to 100 mL/L, 300 mg/L and 600 mg/L of 100 mL diesel wastewater and the adsorption capacity of diesel was determined at different adsorption times from 0 to 300 min at 25°C. The adsorption kinetics of the prepared samples were analyzed by proposed primary reaction (PFO) and secondary kinetics (PSO) as follows:
where the amount of diesel adsorbed at adsorption equilibrium and at time t(min) are recorded as qe(mg/g) and qt(mg/g), respectively. The rate constants of PFO and PSO are k1(min−1) and k2(g/mg min), respectively, and the time is recorded as t(min).
SEM is employed to visualize the surface morphology and microstructure of as-prepared samples, as shown in
The N2 adsorption isotherm and pore size distribution of as-prepared sample was shown in
The XRD pattern is utilized to analyze the crystal structure and phase analysis of the as-prepared sample, as shown in
The surface chemical compositions and surface functional groups of as-prepared samples are analyzed by the FT-IR, as illustrated in
The carboxyl functional group is esterified with the alcohol contained in diesel oil, so it may play a key role in the adsorption of diesel oil [
The adsorption capacities of CSB dose for diesel are shown in
With the increase of the amount of CSB, its binding sites and adsorption capacity will be increased, however, after reaching its peak, the adsorption capacity of CSB would reach saturation, and the adsorption rate will not be further improved. Moreover, too much biochar will make them adhere together in solution, which will also reduce its specific surface areas, the adsorption sites will also be reduced, so that the adsorption rate will even slightly decrease [
In order to study the adsorption equilibrium, Langmuir and Freundlich adsorption isotherm models were employed to evaluate the equilibrium characteristics.
Langmuir | Freundlich | |||||
---|---|---|---|---|---|---|
Temperature (°C) | qL(mg/g) | KL(L/g) | R2 | n | KF(L/g) | R2 |
25 | 451 | 0.679 | 0.996 | 1.263 | 11.48 | 0.968 |
To investigate the kinetic mechanism of diesel adsorption using CSB, kinetic models were fitted to diesel adsorption data at 100, 300 and 600 mg/L diesel concentrations using pseudo-first order (PFO) model and pseudo-second order (PSO) model.
Kinetic model | Parameters | Values | ||
---|---|---|---|---|
100 mg/L | 300 mg/L | 600 mg/L | ||
Pseudo-first-order | qe(mg/g) | 48.77 | 220.06 | 457.86 |
k1(min−1) | 0.019 | 0.022 | 0.026 | |
R2 | 0.959 | 0.941 | 0.981 | |
Pseudo-second-order | qe(mg/g) | 89.45 | 258.24 | 486.32 |
k2(g/mg min) × 10−3 | 0.991 | 0.227 | 0.107 | |
R2 | 0.999 | 0.995 | 0.998 | |
CSB adsorption capacity | qe(mg/g) | 77.7 | 237 | 480.6 |
Adsorbent | qmax (mg/g) | Experimental conditions | Reference | ||
---|---|---|---|---|---|
Adsorbent dose | pH | Time | |||
Crab shell biochar modified by potassium hydroxide | 93.9 | 0.2 g | 7 | 240 min | [ |
Corn husk | 430 | 10 mg/L | 7–8 | 60 min | [ |
Sepiolite modified by tetradecyl trimethyl ammonium bromide (TTAB-Sep) | 434.7 | 7 g/L | 6 | 240 min | [ |
Sepiolite | 190 | 10 g | 6.7 | 1440 min | [ |
CSB | 480.6 | 0.1 g | 7 | 180 min | This work |
In sum, a novel carb shell biochar was prepared by a one-step hydrothermal carbonization and activation method, in which, acetic acid chosen as activator could achieve low-temperature activation. It can be observed from SEM, BET, XRD and FT-IR characterizations that the as-prepared sample is a fluffy irregular layered structure with abundant pores and oxygen-containing functional groups, being beneficial to the adsorption of diesel using CSB. Moreover, the batch adsorption experiments indicate that CSB has high adsorption performances for diesel, and the maximum removal rate is up to 80.1%. And the Langmuir model and the pseudo-second-order model could better describe the adsorption process of diesel using CSB.