| Summary: | 博士 === 中原大學 === 土木工程研究所 === 105 === Nowadays, the vast increase of population and water scarcity are the major challenges in most countries. It has been estimated that approximately two-thirds of the world’s population could encounter absolute water shortages by 2025. Among current technologies, adsorption is widely acknowledged as the most economically favorable technique due to its high removal efficiency, low operation cost, simplicity of design, minimal generation of secondary by-products (e.g., sludge formation), and feasibility for separating a wide range of potentially toxic pollutants from aquatic environments.
In this dissertation, low-cost and renewable adsorbents (i.e., biosorbent, hydrochar, biochar, and activated carbon) derived from lignocellulose wastes (i.e., orange peel (OP), coconut shell (CC), and golden shower pod (GS)) were prepared, characterized, and applied in the removal of several toxic pollutants from aqueous solution. The primary adsorption mechanism is herein proposed.
For cadmium adsorption, an orange peel-derived biochar (OPB) was prepared derived from different pyrolysis temperatures (400, 500, 600, 700 and 800 °C) and times (2 and 6 h). The results demonstrated that the maximum Langmuir adsorption capacity (Qomax) of Cd2+ ions onto biochar slightly increased with an increase in pyrolysis temperature and time. However, this increase did not indicate a statistically significant difference (p>0.01). The Qomax of biochar was found to be 115 mg/g, which was significantly higher than to that of orange peel biosorbent (OP) (54.5 mg/g) and commercial activated carbon (26.5 mg/g). The primary Cd2+ adsorption mechanism onto biochar were Cπ–cation interaction and surface precipitation in the form of (Ca,Cd)CO3 while electrostatic attraction for OP.
A new chemical activation method for the preparation of activated carbon (GSAC) derived from golden shower pod (GS) was proposed. The GSACs prepared from the traditional methods (one-stage and two-stage processes) and new method (three-stage process) were applied in the removal of cation dye from water media. In addition, biosorbents (OP, CC, and GS), hydrochars (OPH, CCH, and GSH), biochars (OPB, CCB, and GSB), and commercial activated carbon (CAC) were applied in removing methylene green 5 (MG5). The prepared GSAC using the proposed chemical activation method exhibited an excellent adsorption capacity (Qomax = 531 mg/g) compared to the GSACs prepared from the traditional methods (253–344 mg/g) and CAC (489 mg/g). Using the same precursor, the Qomax value of GS-derived adsorbent exhibited the following order: activated carbon > biosorbent > hydrochar > biochar. The principal mechanisms that control the MG5 adsorption for biochar and activated carbon are π-π interaction and pore filling. Meanwhile, electrostatic attraction, hydrogen bonding, and n-π interaction were deemed responsible for MG5 adsorption onto biosorbent and hydrochar. The new oxygenation method for surface modification of carbonaceous materials through a hydrothermal process with acrylic acid resulted a decrease in MG5 adsorption and identified to be significant for π-π interactions during adsorption process.
The lignocellulose residue can serve as a potential low-cost and promising adsorbent for efficient adsorption of contaminants in aqueous solution.
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