Rice husk ash (RHA) is a by-product generated by rice mills during the rice drying process, and it is abundantly produced in Malaysia every year. Without proper management can result in severe environmental issues, including water and air pollution. Therefore, in this study, chemical activation process was utilised to convert RHA into porous activated carbon (PAC) which has potential to be used in wastewater treatment. This PAC was produced by chemical activation using different types and concentration (0.5 M, 1.0 M, 1.5 M, and 2.0 M) of activating agents (sodium hydroxide (NaOH), potassium hydroxide (KOH), zinc chloride (ZnCl2) and citric acid) at a lower processing temperature of 80 ℃ for 2 hours. The porosity of the activated carbon is crucial in determining the remazol red (RR) dye adsorption properties. Results indicate that 1.0 M Na-PAC, which is RHA treated with 1.0 M NaOH, demonstrates high performance in both physical and adsorption properties. The BET surface area improved from 54.14 m2/g to 305.27 m2/g, and the pore size from 47 nm to 5 nm. The adsorption isotherm of Na-PAC is fit to Type IV, which is classified as mesoporous were also supported by the SEM image showing presence of the porous structure. Results from the XRD shows the presence of amorphous and crystalline structure which were affected by the silica structure as founded in the FTIR results. Based on this, three different forms of Na-PAC were studied: powder, macrobeads and macroballoons. The macrobeads were prepared by gelation of sodium alginate, while macroballoons used the rolling method, using EPS as a template to produce hollow sphere structure. The adsorption study using UV-spectrophotometer reveals that Na-PAC in powder form possesses a high efficiency of RR dye removal followed by macrobeads and macroballoons with 100 % dye removal at 20, 80 and 120 minutes, respectively. The adsorption equilibrium data of macroballoons and macrobeads were best fitted with the Langmuir adsorption isotherm compared to the Freundlich adsorption isotherm. It shows that the adsorption process occurs in monolayer at the surface of the Na-PAC. Powder and macrobeads forms show good removal efficiency of RR dye, however, both are difficult to manage and separate at the end of the process in the actual application. Therefore, the self-floating properties and adsorption capability of macroballoons give an advantage as the optimised sample to study the effect of different types of binder. Four types of binders were employed (epoxy resin, sodium alginate, silicone resin and grout) to produce macroballoons. Results demonstrated that sodium alginate macroballoon possesses better adsorption with more 80 % of dye removal within 120 minutes as compared to the remaining three binders. This is due to the sodium alginate used did not block the adsorption site on the surface of Na-PAC, meanwhile Na-PAC in grout dispersedly in dye solution, Na-PAC in silicone and epoxy hindered from adsorption process. In conclusion, 1.0 Na-PAC produced high porosity activated carbon that was able to remove the RR dye within the allotted time when applied in three distinct forms for the adsorption process. The types of binder also affect the adsorption ability, giving sodium alginate the most suitable binder to produce macroballoons without hindering the adsorption process.
