Nanotitania crystals induced efficient photocatalytic color degradation, antimicrobial and larvicidal activity

https://doi.org/10.1016/j.jphotobiol.2017.12.005Get rights and content

Highlights

  • Nanotitania crystals were synthesized using aqueous leaf extracts of Euphorbia hirta.

  • Physico-chemical properties of the titanium nanoparticles were characterized.

  • Titania nanoparticles exhibited enhanced photocatalytic dye decoloration activity against 4 important textile dyes.

  • The synthesized nanocrystals showed efficient antibacterial activity against gram-positive and gram negative bacteria.

  • Titania nanoparticles exhibited high larvicidal activity against Aedes aegypti and Culex quinquefasciatus.

Abstract

Textile industries release tonnes of harmful toxic dyes into the environment, causing severe effects on living organisms, including humans. Mosquitoes vectors spread important diseases which cause millions of human deaths worldwide. To control mosquitoes a number of synthetic mosquitocidal agents have been employed but all these pesticides pose harmful effects to human health and non-target species and also led to resistance development in treated vectors. Microbial strains are also developing resistance to the available antibiotics, this currently represents a major public health challenge. The current study is focused on the green synthesis of titanium dioxide nanoparticles (TiO2 NPs) using aqueous leaf extracts of Euphorbia hirta. Results suggested an efficient remedy for the above mentioned problems using TiO2 NPs against the dye degradation, mosquito larvae and bacterial pathogens. The fabrication of TiO2 NPs was confirmed by UV-visible spectroscopy, the biomolecules involved in the synthesis process were evidenced by Fourier transform infra-red spectroscopy (FT-IR), the crystalline structure was observed by using X-ray powder diffraction (XRD) analysis. Spherical shaped TiO2NPs were recorded using field emission scanning electron microscopy (FESEM). Energy dispersive X-ray spectroscopy (EDX) results showed the elemental composition of TiO2 NPs. Enhanced rate of photocatalytic dye degradation efficacy was recorded in in methylene blue (95.8%) followed by crystal violet (86.7%). Antibacterial activity assays indicated growth inhibition was highest in Staphylococcus epidermidis and Proteus vulgaris. The LC50 of TiO2 NPs and E. hirta extract on Aedes aegypti larvae were 13.2 mg/l and 81.2 mg/l, while on Culex quinquefasciatus they were 6.89 mg/l and 46.1 mg/l respectively. Overall, based on the results of the present study, the green engineered nanotitania could be considered as novel and promising photocatalytic, antibacterial, and mosquitocidal agent.

Introduction

Nanotechnologies are receiving a considerable attention in various fields including electronics, UV light emitters, piezoelectric devices, spin electronics, personal care products and agriculture due to their interesting physical, shape-dependent and chemical properties [1], [2]. Nanotechnologies deal with the synthesis and employ of materials smaller than 1 μm, habitually 1 to 100 nm [3]. Usually, nanoparticles are being commercially synthesized either by physical or chemical methods. Nanoparticles synthesized using these methods needs high pressure, temperature, energy or toxic chemicals that are harmful to human health and non-target species [4]. The use of plant-based preparations for the nanoparticle synthesis is a prompt, simple and cheap, environmentally-friendly and a single-step technique involved for bionanosynthesis [5]. The reduction of metal ions into nanoparticles is due to the existence of phytochemicals in plant extracts, this reduce the use of toxic chemicals and high energy inputs [6], [7].

Titanium dioxide (TiO2) is present in nature as the well-known minerals anatase (tetragonal), brookite (orthorhombic) and rutile (tetragonal) and coming under the category of transition metal ions [8]. Rutile is always used in light scattering while anatase is employed in photocatalytic applications. Potential uses of TiO2 nanoparticles (NPs) in several fields subjected them to ecotoxicological studies [9]. Cytotoxicity, phytotoxicity, oxidative stress in plants, microorganisms and lung inflammation in mammals have been reported post-exposure to TiO2 NPs [10], [11]. On the other hand, TiO2 nanoparticle plays a key role in environmental applications due to photo-induced catalytic activity and super hydrophilicity which have been applied to kill bacteria and remove toxic organic substances from water and air, and even in self-cleaning surfaces and for development of gas sensors and in waste water treatment [12]. A survey of earlier literature showed that the leaf extracts from various plants such as Solanum trilobatum, Azadirachta indica and Jatropha curcas have been explored for the synthesis of TiO2 NPs [13], [14], [15].

Euphorbia hirta, commonly known as Asthma weed, is a small medicinal herb distributed in tropical countries belongs to the family Euphorbiaceae. It grows up to 10 cm in height. Its stem is slender and protected with yellowish stiff hairs sometimes reddish in color. Euphorbia hirta leaves are about 5 cm in length and arranged oppositely, usually greenish or reddish in color. The green flowers are dense in small clusters that are found in the middle of the axils and are characteristics of Euphorbia genus. When the plants are cut it produces white milky juice. The portions of the plants have been quantitatively well examined for the presence of diterpenoids, triterpenoids, flavonoids, tannins, phenols with special reference to scopoletin, isocopoletin, quercetin, scoperone, isorhamnetin, pinocembrin, lutelin, kaempferol and gallic acid [16], [17]. Euphorbia hirta is a widely known medicinal plant, which has gained importance in Asian traditional medicine to treat various diseases such as coughs, diarrhea, dysentery and ear infections. The ethanolic and methanolic extracts of the plant are known for their antibacterial and antifungal activity [18], [19].

Mosquito-borne diseases are key main causes for fatality every year worldwide [20]. These vectors can transmit important diseases, namely malaria, dengue, chikungunya, Japanese encephalitis, yellow fever, lymphatic filariasis and Zika virus. Also, mosquitoes lead to further problems from a public health standpoint due to the risks associated with the use of chemical insecticides, toxicity to non-target organisms and unavailability of vaccines for many mosquito-borne diseases [21], [22]. The only available option to diminish the prevalence of vector-borne diseases is an effective control of mosquito populations [23]. Aedes aegypti is one of the leading mosquito vectors which carry dengue, chikungunya, Zika virus and yellow fever [24]. In the year 2009, World Health Organization reported that the two-fifths of the world population are under the risk of dengue (WHO index) and 28,292 cases of infection and 108 deaths were reported in India in the year 2010. Culex quinquefasciatus is an important vector of lymphatic filariasis, since transmits Wuchereria bancrofti and is also able to transmit Ross River virus and West Nile virus. Currently, about 120 million people are being infected by filariasis globally Chemical insecticides are environmentally harmful, highly toxic and also led to resistance development. The use of biopesticides such as herbal formulations may be an effective. Previous studies showed the toxicity of ethyl acetate, butanol and petroleum ether extracts of E. hirta tested beside early fourth instar larvae of A. aegypti and C. quinquefasciatus [25].

The biological combination of silver nanoparticles with Euphorbia hirta leaf extract metabolites and the related antimicrobial activity was studied on Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Metal oxide nanoparticles, particularly TiO2 show high antibacterial effects [26], [27]. TiO2 induced bactericidal activity was due to oxidative damage occurred in the bacterial cell wall. With TiO2 exposure to ultraviolet irradiation reactive oxygen species releases of O2, OH, H2O2 and HO2 have been reported, along with severe damages to polyunsaturated phospholipids in bacteria [28].

The photocatalytic properties of some materials have been applied to convert solar energy into chemical energy, to oxidize or reduce materials, to get useful materials such as hydrogens, or hydrocarbons and to eliminate pollutants [29]. TiO2 has unique photocatalytic activity. Among the polymorphs of TiO2, anatase TiO2 shows effective photocatalytic activity due to its high absorption ability in organic-contaminated solutions, molecular oxygen and low rate of recombination of electron-hole pairs [30]. This photocatalytic activity of TiO2 has been utilized for the degradation of industrial organic dyes. Dyes and pigments are commonly used for the industrial coloring of cloth, paper, cotton, wool, silk, leather, and nylon. Dyes are either toxic or mutagenic and carcinogenic owed to the presence of metals and other chemicals in their structure [31]. Normally used basic dyes are in a group of complex organic materials basically found in the form of chromophore structure [32]. There are > 10,000 commercially available organic dyes with over 7 × 105 tons of dyestuff produce annually around the world [33]. With the increased use of a wide variety of dyes also increases the environmental pollution day by day. Various dyes are stable to light and not that much easy to degrade biologically [34]. In order to prevent the accumulation of hazardous materials/pollutants into the environmental including organic dyes, it is unavoidable to treat them before releasing it into the environment. Usually, chemical and physical processes have been used to treat the dyes however these processes are quite expensive and cannot be used effectively. TiO2 is widely used as a photocatalyst because of its superior stability in UV-light and water. In this study, TiO2 NPs were engineered by green chemistry approach using the E. hirta leaf extracts, and used for the degradation of methylene blue, methyl orange, alizarin red and crystal violet.

Overall, the objectives of the present studies were (i) phytofabrication of TiO2 NPs using E. hirta leaf extracts and their characterization, (ii) evaluation of synthesized TiO2 NPs as nanocatalyst in degradation of dyes, (iii) estimate of nanoparticle toxicity against human microbial pathogens, and (iv) investigate the toxicity of TiO2 NPs on larvae of Culex and Aedes mosquito vectors.

Section snippets

Bioengineering of TiO2 NPs and their Characterization

Undamaged fresh and healthy leaves of Euphorbia hirta were collected from the campus of Periyar University, Salem, Tamil Nadu, India. The leaves were rinsed with tap water to clean the impurities, followed by washing with sterile distilled water. Green synthesis of TiO2 NPs was carried out by using plant extracts prepared via microwave irradiation. About 20 g of healthy leaves were chopped into small pieces and grounded with the help of a mortar and pestle. The homogenized leaves were mixed with

Biofabrication and Characterization of TiO2 Nanoparticles Using E. hirta Leaf Extracts

This investigation was focused on bioengineering and characterization of TiO2 NPs using E. hirta leaf extracts prepared via microwave irradiation procedure and evaluation of their mosquito larvicidal, antimicrobial and photocatalytic efficacy. The addition of E. hirta leaf extract to the TiO4 solution resulted in a rapid color change of the reaction mixture from green to brown due to the formation of TiO2 NPs after 24 h of incubation under sun light irradiation. However, no color change was

Conclusions

Overall, this report describes the green chemistry approach to produce nanotitania by using aqueous leaf extract of E. hirta. The effective green synthesis of TiO2 NPs was verified by optical and morphological characterization, i.e., UV–visible spectrophotometry, Fourier transform infrared spectroscopy, X-ray diffraction, field emission-scanning electron microscopy and energy-dispersive X-ray spectroscopy techniques. The mosquito larvicidal toxicity of titanium oxide nanoparticles and E. hirta

Conflict of Interest

The authors declare that they have no conflict of interest.

Acknowledgements

The authors thank Periyar University for providing necessary facility to this project.

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