The Physical and Optical Studies of Crystalline Silica Derived from the Green Synthesis of Coconut Husk Ash

Abstract

The green synthesis of silica has been extensively explored over the last few decades, as silica compounds found in commercial products can cause negative effects on human health. This calls for alternative ways to produce silica that are safer, cheaper and more environmentally friendly. Some of the agricultural wastes proven to contain silica include rice husk, sugarcane bagasse, coconut shells and coconut husk. This paper describes the synthesis of silica from coconut husk waste, and its physical and optical properties for potential utilization in optical applications. Coconut husk was subjected to fire at 500–700 °C so as to form coconut husk ash (CHA), and was then treated with sulfuric acid to extract silica from the ash. Most of the weight degradation subsequently occurred at temperatures from 221 to 360 °C. X-ray fluorescence (XRF) analysis proved that 91.76% of the silica was obtained, while major peaks on the X-ray diffraction (XRD) spectrum were observed after the acid treatment. Chemical bonds such as Si-O-Si, CH2, -OH and Si-OH were found in the spectrum of the Fourier transform infrared spectroscopy (FTIR). Furthermore, the particles displayed rod-like shapes and irregular sizes, but the particle with sizes ranging from 200–750 nm decreased after the acid treatment. The relationship between the absorption coefficient and photon energy was obtained by finding the optical energy gap, which was found to be 4.3 eV. These data points provide critical information when used in optical applications. The overall studies show that synthesized silica has great potential for use in optical field applications.

Synthesis and Characterization of ZnO-SiO2 Composite Using Oil Palm Empty Fruit Bunch as a Potential Silica Source

“…The mechanism involves the existence of carboxyl groups in sulfuric acid that tend to donate protons, hence forming the negatively charged carboxyl group. These negatively charged carboxyl groups can form stable complexes with positive charged ions, Ca + and K + , that are present in the palm ash [ 25 ]. This is the reason why the impurities of the palm ash were reduced, as can be observed in Table 2 .…”

“…The presence of SO 3 was due to the reaction of sulfuric acid used for leaching. These results indicate that leaching can increase the percentage of SiO 2 in palm ash and remove part of the metal impurities in the sample [ 25 ].…”

Sustainable Production of Arecanut Husk Ash as Potential Silica Replacement for Synthesis of Silicate-Based Glass-Ceramics Materials

“…The initial stage (I) of the weight loss corresponds to the release of moisture from the arecanut husk. At this stage, about 8.97% of the total weight of arecanut husk decomposed due to loss of water content and light volatile compounds [10][11][12]. Afterward, the second stage (II) of weight loss occurred in the range of 200 • C-315 • C. Above 200 • C, the thermal resistance of agriculture waste gradually [13].…”

Optical studies of crystalline ZnO–SiO2 developed from pyrolysis of coconut husk

“…ZnO nanopowder (99.99%) (US Research Nanomaterials, Inc., United State of America) with range size of 10-30 nm and coconut husk ash (CHA) was used as the starting materials in this work. CHA was obtained from burned coconut husk at 700°C for 2 h and after that undergone acid leaching process by sulphuric acid (H 2 SO 4 ) to increase the silica composition to 91.76% [19]. ZnO and CHA were mixed together for 1 day using ball milling process to ensure the homogeneity of the mixed composition.…”

“…Various researches have been conducted to 'recycle' bio-waste into materials that have potential to be used in certain applications. Among them were rice husk [2][3][4][5][6], rice straw [7][8][9][10], banana peel [11], corn cob [12,13], palm waste [14,15], sugarcane [16], turmeric [17], and coconut husk [18,19]. Raw materials silica (SiO 2 ) is one of the elements presents in most agricultural waste and commonly used in numerous researches for optical application especially in phosphors materials production.…”