Influence of Aloe vera and Pluronic F127 on the enhancement of Photocatalytic degradation and Antibacterial activity of ZnO by sol-gel synthesis method

: The development of plant-based photocatalyst with a minimum time of irradiation for water-soluble dye disposal from industries is a great significance to unravel water pollution. In the present work, the sol-gel synthesis method was employed for the synthesis of zinc oxide nanoparticles using Pluronic F127 and Aloe vera as dispersing media. A hexagonal wurtzite structure and surface morphology confirmed by XRD and FE-SEM analysis. The infrared study was applied to substantiate the acceptable compounds within the nanoparticles and phytochemicals presence within the extract. From the DRS spectra, Bandgap energy of ZnO nanoparticles (3.22eV) was decreased to 2.89eV by blending of Aloe vera and Pluronic F127 into ZnO. The photocatalytic action of different combinations of ZnO was examined against malachite green dye under UV light and visible light irradiation. Upto 95% degradation was achieved for ZnO/ Aloe /PF127 with a minimum time of UV light exposure. All combinations of ZnO showed effective bactericidal activity against multi-drug resistance of E.coli, S.aureus, B.subtilis, and P.aeruginosa . These findings proved the overwhelming photocatalytic and antibacterial activity of ZnO samples, which might be used as effective remediation to treat textile dye wastewater.

attention because of its excellent chemical and photochemical stability, biological activity, nontoxicity, low cost, and enormous exciton separation energy [3].
Due to the non-toxic behavior of ZnO nanoparticles, it is often used as antimicrobial agents towards several disease causing pathogens. The synthesis of nanoparticles using plant extract may be the cleanest and safest method compared to other physical and chemical synthesis methods [4,5]. Among various syntheses of nanoparticles from plant extract, Aloe vera contains plenty of flavonoids, terpenoids, amino acids, enzymes, vitamins, and polysaccharides. The presence of these compounds in Aloe vera can give non-toxic behavior with excellent reducing agent property. The green fuel of Aloe vera was chosen according to this direction for the preparation of ZnO nanoparticles. Several numbers of metal oxides synthesized from plant extracts have been reported [6][7][8][9]. Besides of surfactants for the synthesis process may increase their optical and biological activities. Pluronic F127 based TiO2 mesoporous was prepared by 4 Emy Merlina Sumsudin et al. in 2015 and revealed that the physicochemical properties changed due to the addition of Pluronic F127 and ends up in an enhanced photocatalytic activity [10].
The present work focused on the synthesis of different combinations of ZnO using Pluronic F127 and Aloe vera to evaluate the photocatalytic degradation of malachite green dye.
In addition, antibacterial activities have been studied with several disease causing Gram-negative and Gram-positive pathogens.

Preparation of Aloe vera gel powder
Fresh and matured Aloe vera leaf was washed several times with DI water to get rid of dust particles; gels were separated and dried at 40°C using hot-air oven for two days. The prepared gel powders with the help of mortar and pestle were stirred with DI water for four hours, filtered, and stored for the further synthesis process.

Synthesis of different combinations of ZnO
The aqueous solution of Pluronic F127 (EO100PO65EO100) was prepared with 1:4 ratios at the continuous stirring of an hour to obtain a homogeneous solution. Both Aloe vera gel powder and Pluronic F127 solutions were drop-wisely added into 1M of zinc acetate under continuous shaking for six hours at 70°C. The obtained ZnO/Aloe/PF127 precipitate was washed three-five times with DI water and annealed at 350°C for an hour in a muffle furnace. For ZnO and ZnO/PF127, NaOH was added for the synthesizing process.

Characterization Methods
The structure and size of different combinations of ZnO was characterized by X-ray diffraction (XRD) analysis (PANalytical X'PERT PRO) in a continuous scanning mode of 2θ=10°-80° at room temperature. The functional groups present in the synthesized nanoparticles were determined by Fourier Transform Infrared Spectrometer (FTIR) (Shimadzu). The morphologies were examined by FESEM (MIRA3 TESCAN). The optical properties were studied by UV-DRS (SHIMADZU) and Spectrophotoflurometer-RF 5301PC instrument.

Photocatalytic experiments of MG dye and textile dye wastewater
The photocatalytic activity of MG dye aqueous solution was tested by different combinations of ZnO. In this process, 0.04g of the catalyst is added into 250 ml of MG dyecontaining aqueous solutions and sonicated for 30 minutes in dark condition to ascertain the adsorption-desorption equilibrium of MG and ZnO. In the next step, the suspension is exposed to Where the percentage of degradation is denoted as Ƞ, the initial and after irradiation of selected time interval of concentration of dye ( ) is denoted as 0 . To inspect the reusability and photo-stability, the cycling experiment of MG aqueous solution was conducted using an oven drying method under UV light irradiation.

Antibacterial activity
The

Size and structural analysis
Powder X-ray diffraction was performed to analyze the crystalline phase of different combinations of ZnO nanoparticles. The average crystallite size was calculated by following Debye Scherer's equation.

= ⁄ ……………………. (3)
Where D represents the average crystallite size, λ represents the wavelength of X-ray   showed low agglomerated hexagonal and rectangular structure because of the Aloe vera and PF127 surfactant incorporation within the sample of the synthesized ZnO/Aloe/PF127.

Vibrational Studies-FTIR
To ascertain the formation of zinc oxide in ZnO/PF127, and ZnO/Aloe/PF127 and their interaction with PF127 and Aloe vera, the samples were analyzed by FTIR spectroscopy within the range of 400-4000 cm -1 at room temperature, as shown in Fig. 2. Metal oxides generally give their peak between 400 cm -1 to 600 cm -1 . In this stance, the lower wavelength vibration peak of 462 cm -1 in all combinations of ZnO strongly attributed to the ZnO vibration mode [21]. The 1458 cm -1 and 1519 cm -1 peaks were represents the symmetric and asymmetric stretching vibration of the C=O group and it corresponds to the zinc acetate used for the synthesis process [22]. ZnO peaks observed in all spectra with their wavelength slightly shifted and the new peaks were also observed because of the blending of PF127 and Aloe vera into ZnO.
The vibrational peaks at 1111cm -1 , 1342cm -1 , 1280cm -1 and 2885cm -1 were attributed to the C-O stretching, C-H bending, -CH2 twist, and C-H stretching vibration, which confirms the presence of PF127 in both ZnO/PF127 and ZnO/Aloe/PF127 spectra [23][24][25]. For ZnO/Aloe/PF127, 1242cm -1 , 1743cm -1 , 2978cm -1 peak correspond to the C-O-C stretching of -COCH3 groups, and presence of carbonyl group in the Aloe vera. The interaction of phytochemicals such as alcohols, phenols, amines, and carboxylic acids with zinc surface and aid in the stabilization of ZnO was confirmed by the above peaks [7,26]. The presence of hydroxyl groups and bending vibration of absorbed water on the photocatalyst surface was confirmed by the vibration bands at 1558cm -1 and 3417cm -1 in all spectra which could help to capture the holes in the valence band and helps to increase the number of hydroxyl radicals [22]. The presence of water molecules in all combinations of ZnO were confirmed by 3000 cm -1 -3650 cm -1 peak. eV, 3.02 eV, and 2.89eV for ZnO, ZnO/PF127, and ZnO/Aloe/PF127 respectively, illustrated in Fig. 3 (a, b, and c) inset shows reflectance, which attributed to the smaller crystallite size quantum confinement effects [7,17]. The surface to volume ratio was increased with decrease in crystallite size, which increases the defect distribution of nanomaterials surface and exhibited strong absorption bands. The blending of PF127 and Aloe vera into the ZnO shifting the photocatalytic action from the UV region to the visible region due to the bandgap energy decrease, thus red-shift occurs [23][24][25][26][27].
The photoluminescence emission spectra of ZnO samples (excitation wavelength of 380 nm) were carried out to determine the separation and recombination of photo-generated electrons and holes in the catalyst. Generally, semiconductor materials have two photoluminescence emissions (excitonic and trapped). The sharp and near absorption edge peak is called excitonic emission while broad peaks are called trapped emission which is found at a longer wavelength [28]. In Fig. 3 (d), three characteristic excitonic peaks around 423 nm, 438 nm, and 467 nm (Blue emission) were observed in every sample [25,27] which was mainly due to the surface defects and oxygen vacancies of ZnO. In another, the broad peak at ~ 517 nm (Green emission) was assigned to the defect-related emission because of the recombination of photo-generated holes with singly ionized oxygen vacancies of ZnO. The decrease in PL emission intensity value indicate longer lifetime of photo-generated − − ℎ + efficiency and weaker recombination, which result in the higher photocatalytic performance [19,29,30].

Photocatalytic degradation of Malachite Green dye
The photocatalytic performance of all combinations of ZnO was investigated for the  Fig. 4 (a, b). This demonstrates that the ZnO/Aloe/PF127 exhibits excellent photocatalytic activity because of the lower crystallite size, active surface area, bandgap energy, and structure. [35]. In the same way, V.K Patel et al., in 2017 have been reported the synthesis process of ZnO nanorods using Aloe vera and PEG (8000) and investigate their catalytic effect by thermal decomposition of potassium perchlorate under the sono-emulsion route method. The results reported that the synthesized ZnO nanorods using Aloe vera with PEG exhibited higher catalytic activity compared to ZnO nanorods from PEG (8000) because of the large number of surface hydroxyl groups, amino acids, and phenolic compounds presence [36]. And another report, Nikhil Chauhan (2019)

Conclusions
The different combinations of ZnO nanoparticles were synthesized employing sol-gel synthesis method. The synthesized samples were characterized by XRD, FESEM, UV-DRS, FTIR, Photocatalytic and Antibacterial activity to investigate the structural, morphological, optical, and biological properties. The increase in degradation level might be due to the bandgap energy value and crystallite size of ZnO nanoparticles. The lower crystallite size value will give a higher surface to volume ratio, which results an enhancement of photocatalytic degradation efficiency. The photocatalytic degradation efficiency of 95% was achieved for ZnO/Aloe/PF127 at a minimum time (20 min) of UV light irradiation. Furthermore, the antibacterial investigation of all combinations of ZnO showed effective antibacterial activity against various disease causing microbes. The above characterization results prove that the ZnO/Aloe/PF127 can be used to degrade several effective dyes. This can be also used for water purification of textile industry.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.