Activated Carbon from Agricultural Wastes for Adsorption of Organic Pollutants

Abstract

Agricultural waste materials (strawberry seeds and pistachio shells) were used for preparation of activated carbons by two various methods. Chemical activation using acetic acid and physical activation with gaseous agents (carbon dioxide and water vapor) were chosen as mild and environmentally friendly methods. The effect of type of raw material, temperature, and activation agent on the porous structure characteristics of the materials was discussed applying various methods of analysis. The best obtained activated carbons were characterized by high values of specific surface area (555–685 m2/g). The Guinier analysis of small-angle X-ray scattering (SAXS) curves showed that a time of activation affects pore size. The samples activated using carbon dioxide were characterized mostly by the spherical morphology of pores. Adsorbents were utilized for removal of the model organic pollutants from the single- and multicomponent systems. The adsorption capacities for the 4-chloro-2-methyphenoxyacetic acid (MCPA) removal were equal to 1.43–1.56 mmol/g; however, for adsorbent from strawberry seeds it was much lower. Slight effect of crystal violet presence on the MCPA adsorption and inversely was noticed as a result of adsorption in different types of pores. For similar herbicides strong competition in capacity and adsorption rate was observed. For analysis of kinetic data various equations were used.

Mesoporous Carbons of Well-Organized Structure in the Removal of Dyes from Aqueous Solutions

“…The difference in the respective surface area values between the SAXS data and the low-temperature nitrogen sorption data may indicate a pore area inaccessible to nitrogen molecules and thus inaccessible to the adsorbate in adsorption applications. These observations are consistent with the literature reports [ 36 , 56 ].…”

“…Some studies on adsorbing performance of various materials for the studied dyes and the corresponding maximum adsorption capacities have been reported [ 25 , 26 , 33 , 36 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ], which are listed in Table 4 . Compared with referred materials, the mesoporous carbons obtained by impregnation of well-organized silicas proved to be similar or even more efficient adsorbents.…”

“…Therefore, several methods for the synthesis of mesoporous activated carbons based on a large variety of the natural or synthetic precursors were proposed. The simple method of preparation of mesoporous activated carbons is a direct pyrolytic carbonization, followed by physical activation with gaseous agents (carbon dioxide, water vapour) [ 36 ]. To improve the mesoporous structure of the final product the second activation is advisable in a fluidized bed reactor [ 37 ].…”

Physicochemical and Adsorption Characteristics of Divinylbenzene-co-Triethoxyvinylsilane Microspheres as Materials for the Removal of Organic Compounds

“…The Pore Diffusion Model (PDM, McKay) describe adsorption on porous solids which combines the transfer resistance of adsorbate particles through the surface layer, the proportional penetration of the adsorbate into the adsorbent grains, the sharp boundary between the space in which the equilibrium state is determined and the space without the adsorbate, and can be expressed by the mathematic formula: where u eq is the relative adsorbate loss, the parameter B = 1 − 1/ B i and B i = K f / D p is the Biot number, D p is the pore diffusion coefficient, K f is the external mass transfer coefficient, τ s is the undersized model time [ 32 , 56 , 57 ].…”

“…Among the different wastewater treatment methods, adsorption is widely used because of its simplicity, good treatment efficiency, the availability of a wide variety of adsorbents, and relatively low costs. Aliphatic or aromatic organic substances including aldehydes, amines, nitrides, pesticides, pharmaceuticals and dyes are generally compounds that are difficult to decompose in water [ 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. Therefore, the development of effective, inexpensive and selective sorbents is a crucial issue.…”