Zinc oxide from aloe vera extract: two-level factorial screening of biosynthesis parameters.

Authors Nurul Izwanie Rasli a , Hatijah Basri a,* , Zawati Harun b

Zinc oxide (ZnO) was biosynthesized from aloe vera plant extract. The aloe vera plant extract was used as a reducing agent in biosynthesis process. Green synthesis method was proposed because it is cost effective and environmentally friendly. ZnO was characterized using SEM, EDX, FTIR, and XRD analyses. The antibacterial property was tested against Escherichia coli. The effects of aloe vera volume (2–50) mL, precursor concentration (0.001–0.300) M, reaction time (20 min–48 h), and temperature of the reaction (26–200) “C on ZnO characteristics were investigated and screened using a two-level factorial method. Based on the observation and ANOVA analysis result, precursor concentration was the only significant parameter that affected the production of the ZnO nanoparticles (NPs). The EDX analysis proved the presence of ZnO while the SEM analysis confirmed the average size of ZnO particle size was in the range of (18–618) ?m with a rod-shape appearance. The XRD analysis showed that the average crystallite size was 0.452 ?m and it was in the hexagonal phase. It was also proven to have antibacterial property against E. coli. Nanomaterial research has been developing rapidly and has potential in various areas, including biomedical, magnetics sciences, biosensors, optoelectronics, and catalysis. In the past years, green synthesis of nanomaterials such as silver, zinc oxide, magnesium oxide, gold, cerium oxide, copper oxide and titanium dioxide has been conducted extensively due to simple work-up procedure, environmentally benign nature, reusable, low cost, and ease of isolation. The biosynthesized NPs are also stable, capped by the biological compound, robust, and economical compared to other NPs produced by standard techniques. ZnO is one of the most valuable nanomaterials and is potential to be used in the industry. Furthermore, ZnO has been recognized as safe to be used as a food additive by the Food and Drug Administration (FDA). ZnO possesses a wide bandgap yield (3.37 eV) and high excitation binding energy (60 meV) in which it absorbs a larger reaction of the UV spectrum and exhibits a greater photocatalytic performance than TiO2 in the photodegradation of organic pollutants. Physical, chemical, and biological methods have been used to synthesize ZnO particles. The synthesis route determines the properties of the produced NPs in terms of its crystal growth, morphology, size, size distribution, stability, and aggregation. Due to the increasing popularity of biological methods, different sources like bacteria, fungus, algae, and plants have been used to produce ZnO NPs. Plant extract is used as an aid in the synthesis of NPs as it is cheap and safe to the environment. Various works on the use of plant extract to synthesize ZnO NPs have been reported. Aloe vera is also well known for its medicinal properties and has been used as a soothing agent for burn and inflammation. Furthermore, the therapeutic properties of aloe vera have been employed in the commercial applications of pharmaceutical, food, and cosmetics. The extract of aloe vera plant has been used for the synthesis of gold, silver, copper oxide, indium oxide, titanium dioxide, cerium oxide, and tin oxide. Biosynthesis of ZnO using aloe vera extract, the biosynthesis of ZnO was conducted by applying a screening step using two-level factorial experimental design with the aid of Design Expert software. The purpose of the screening steps was to determine the parameters that influenced the production of the nanoparticles. Four parameters were studied, namely aloe vera volume, reaction time (stirring time), precursor concentration, and temperature. Antibacterial activity. After 24 h of incubation, the active inhibition zone measured was around 1.325 mm2. The existence of inhibition zone clearly indicates the involvement of membrane disruption and leads to the death of pathogens. ZnO is a well-known antibacterial agent and effective at very low concentration of bacteria as confirmed by previous studies. In addition, the small size of the biosynthesized ZnO provides a large surface area and this leads to more contact between the NPs and the bacterial cells. From the result, the biosynthesized ZnO from aloe vera plant extract has been proven to have antibacterial property, the biosynthesized NPs at various concentrations of 2–12 mM reacted against bacteria such as Staphylococcus aureus, Serratia marcescens, Proteus mirabilis, and Citrobacter freundii and as well as fungi like Aspergillus flavus, Aspergillus nidulans, Trichoderma harzianum, and Rhizopus stolonifera.