A Novel Green Synthesis of Au/TiO2 Nanocomposites

Prof. Lahiru A. Wijenayaka, Sri Lanka Institute of Nanotechnology (SLINTEC), Mahenwatte, Pitipana, Homagama, Sri Lanka and his collaboration team has reported on the interesting materials for effective environmental alternative remediation via nontoxic, low cost and eco-friendly methods dedicated to the scientific community. Here, a novel, facile, and green synthetic approach to synthesize gold nanoparticle decorated over TiO₂ (Au/TiO₂) nanocomposites for sustainable environmental development has been discussed [1].

Based on various metal oxide semiconductor (MOS) photocatalysts, titanium dioxide (TiO₂) is the most widely used, owing to its effective and excellent results in optical transmittance, high refractive index, chemical stability, concurrently being stable, nontoxic, and inexpensive [2]. They are highlighted with the following points: (i) Synthesis of the Au/TiO₂ nanocomposite, (ii) Microscopic characterization, (iii) Dye adsorption on Au/TiO₂ and (iv) Photocatalytic dye degradation on Au/TiO₂. The general changes of charge recombination time in TiO₂ has been estimated to be in the order of 10⁹ s, while the chemical reaction time shows the fast responses of recombination between photogenerated charges with any adsorbed species is 10⁸ to 10³s [3]. Hence, the photocatalytic reactivity of some species adsorbed on the surface of nanoparticle (TiO₂) catalyst. Therefore, the metal oxide is far from being a perfect and established photocatalyst regardless of its new trend and widespread applications.

Bio-comfortable and bio-compatibility of nanoscaled materials preparation may be a significant role to enhance via the utilization of biogenic synthetic pathways, the use of microorganisms or plant-based extracts [4]. Although the incorporation of Gold nanoparticles (AuNPs) to the surface of TiO₂ thus enhancing the photocatalysis part of the latter is well demonstrated, there is no past resultant accountability of sustainable green methodologies to develop such eco-friendly and innocuous nanocomposite/nanomaterials. In addition, many recent scientific and knowledgeable efforts have been focused on the preparation of novel nanosized materials with the support of the light assisted degradation of unwanted contaminants; or photocatalysis. Hence, other mechanisms are handled with effective contaminant capture and removal which can be conducted, such as surface adsorption which is facile and spontaneous, are relatively less exploited [5].

Figure 1. Schematic diagram of the green synthesis of Au/TiO₂ [1].

The preparation of AuNPs decorated TiO₂ nanocomposite using an entirely green chemical synthesis approach has been reported. AuNPs were synthesized by reducing tetrachloroauric(III) acid (HAuCl₄) onto TiO₂ particles using a green tea extract. Green tea acts here as both reducing and stabilizing agents, thus obviating the need to utilize any auxiliary chemicals during the preparation and/or the application of the catalyst.

The novel facile green synthetic methodology for the preparation of Au/TiO₂ nanocomposite using the following selective precursors were Titanium dioxide (TiO₂) (anatase), tetrachloroauric(III) acid trihydrate (HAuCl₄ 3H₂O) and the green tea extract contained a mixture of polyphenols (like catechin, epicatechin, epicatechin gallate, gallocatechin, and gallocatechin gallate, as well as caffeine, gallic acid and theophylline) [6, 7]. Based on the modern green method, the utilized conditions used for the reduction of Au³⁺ into the AuNPs were previously reported with experimental and optimized one. (i) the resultant material of AuNPs expressed with uniform size and morphology, (ii) green tea serves dual roles of a reducing and a stabilizing agent, (iii) preventing the need for any auxiliary chemical species, and (iv) under mild temperature conditions (50º C). Photocatalytic testing held with the dye degradation on Au/TiO₂ with same volumes of Au/TiO₂ nanomaterial suspension (250 ppm) and a methylene blue (MB) sample solution. The mixed samples were utilized under UV light exposure with and without nanomaterials. In contrast, for Au/TiO₂, there was no significant absorbance in the supernatant until the MB concentration reached 17 ppm. To conclude, they repeated the experiment much times for different durations of UV irradiation and bare TiO₂. Experimental evidence identified that the Au/TiO₂ show a superior adsorption capacity of 8185 mg g^-1 towards methylene blue (MB) in sample solutions, while the photocatalytic rate constants for the degradation of MB on the substrate expressed 4.2-fold improvement compared to bare TiO₂.

Scientific development of nanocomposite (Au/TiO₂) with suitable light mediated reaction scenario would be concluded in two distinct and independent pathways are namely (1) surface adsorption and (2) photocatalysis. They have insisted on these chemical reactions for the efficient removal of waste contaminants from the various samples (in aqueous) environmental situations.

AuNP decorated titania was highlighted with the enhancing nature of photocatalytic activities by facilitating efficient electron transfer reactions. They identified that a photocatalyzed chemical reaction resulted in a synergetic effect, during the removal of non eco-friendly chemicals (hazardous) from the contaminated sample waters.

Our SNB Team recommended this research article to enrich our reader’s knowledge about the novel green synthesis of gold decorated TiO₂. They improved the capacity to capture as well as degrade MB in sample solution indicates that the Au/TiO₂ nanocomposite has outstanding potential to serve in sustainable environmental remediation. The ability of Au/TiO₂ to be used in environmental remediation via enhanced nanocomposite surface adsorptions and ensuring photocatalysis was investigated using methylene blue (MB) as a model dye. Here, a clear understand of Au/TiO₂ nanocomposite developed via the possibility of facile and green route represents the atom economy, stability concept, prolonged storage, the superior adsorption capacity of 8185 mg g^-1for MB, significant potential for waste contaminant capture, and significantly enhanced photocatalytic degradation rate of MB. The overall theme says that material is suitable to support the environmental applications system.

References

M. Perera, et al., RSC Adv., 10, 29594 (2020).
Y. Zhao,et al., Mater. Lett., 61, 79 (2007).
M. Ni, et al., Renewable Sustainable Energy Rev., 11, 401 (2007).
S. Aswathy, et al., Spectrochim. Acta, Part A, 97, 1 (2012).
H. Wang, et al., Appl. Surf. Sci., 360, 840 (2016).
S. P. J. Namal Senanayake, J. Funct. Foods, 5, 1529 (2013).
M. Farahat et al., Br. Poult. Sci., 57, 714 (2016).

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Dr. S. Thirumurugan

National College, Tiruchirappalli

Tamil Nadu, India

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