Photocatalytic Degradation of Ethylene Emitted by Fruits with TiO 2 Nanoparticles
Murid Hussain, †,‡ Samir Bensaid, † Francesco Geobaldo, † Guido Saracco, † and Nunzio Russo*,† Department of Materials Science and Chemical Engineering, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129Torino, Italy, and Department of Chemical Engineering, COMSATS Institute of Information Technology Lahore Campus, M. A. Jinnah Building, Defence Road, Off Raiwind Road, Lahore 54000, Pakistan
The photocatalytic degradation of ethylene (emittedby fruits) by novel TiO 2nanoparticles (TNPs),at 3°C, has been investigated to consider the possibility of its use for the cold storage of fruits. TNP exhibits a high speciﬁc surface area, a good anatase-to-rutile mixed phase ratio, and more surface OH groups than commercially available Degussa P 25, as characterized by nitrogen adsorption, static light scattering, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. TNPs, tested in an ad-hoc designed Pyrex glass photocatalytic reactor, showed higher photodegradation activity of ethylene than Degussa P 25. The superior characteristics of TNPs, compared to Degussa P 25, might induce the adsorption of ethylene and water and the generation of OH groups which act as oxidizing agents on the TNP surface, leading to higher photocatalytic activity. In the absence of water the photocatalytic degradation of ethylene reduced signiﬁcantly. Moreover, a positive effect was observed when UV light was converged on the catalyst and an increase in ethylene degradation was achieved when UV light converging pipes and lens were used.
Ethylene (C2H 4) is an odorless and colorless gas which exists in nature and is generated by human activities as a petrochemical derivative, transportation engine exhausts, and thermal power plants. 1,2However, naturally it is produced by plant tissues and biomass fermentation and occurs along the food chain, in packages, in storage chambers, and in commercial big refrigera-tors. 3The effect of ethylene on fruit ripening and vegetable senescence is of signiﬁcant interest for the scientiﬁc community. Ethylene confers both positive and negative effects during fruit ripening. 1Among the positive effects, ethylene stimulates the ripening process of climacteric fruits (apples,apricots, avocados, bananas, peaches, plums, and tomatoes), resulting in desirable ﬂavors, colors, and texture (qualitycharacteristics). In these kinds of fruits, negative effects can be found during postharvest storage, due to an acceleration of the ripening process (overripefruits), leading to fruit quality loss. 4-7During the postharvest storage of fruits and vegetables, ethylene can induce negative effects such as senescence, overripening, accelerated quality loss, increased fruit pathogen susceptibility, and physiological disorders. Fruits, vegetables, and ﬂowers have ethylene receptors on their surface. Their actuation promotes ethylene production by the fruit itself and accelerates its ripening and aging. 2Thus, preventing postharvest ethylene action is an important goal.
Literature shows some conventional as well as commercial techniques and technologies to control the action of ethylene. The most common are ethylene scavengers, especially the potassium permanganate (KMnO4) oxidizer. 8However, KMnO 4 cannot be used in contact with food products due to its high toxicity. Ozone (O3) is also an alternative oxidant, 9but it is highly unstable and decomposes into O 2in a very short time. Carbons and zeolites are used as ethylene adsorbers and play a key role in the control of ethylene. 3,10,11This technique only transfers the ethylene to another phase rather than destroying it. Hence, additional disposal or handling steps are needed. There are also some other alternative, attractive, but expensive materials 12or techniques, 13but the problem is cost effectiveness. Photocatalytic degradation of hazardous materials is one of the most desirable and challenging goals in the research of the development of environmentally friendly catalysts. 14,15It in-volves the actual destruction of organic contaminants rather than just the transfer of a contaminant from one phase to another. In the present work, we have focused on the use of novel TiO 2nanoparticles (TNPs)photocatalyst for ethylene degrada-tion in fruits and vegetable cold storage, at low temperature, with the help of the new fabricated photocatalytic reaction system. An efﬁcient way of utilizing this photocatalyst, which has superior characteristics for the target application, has been developed. Materials characterizations have been performed through speciﬁc surface area analysis, X-ray diffraction (XRD), static light scattering (SLS),energy dispersive X-ray spectros-copy (EDX),Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS)in order to analyze the reaction. The photocatalytic activity of the TNP has also been compared with that of Degussa P 25TiO 2.
2. Experimental Section
2.1. TNP Photocatalyst Synthesis. New TNPs were syn-thesized at a large scale (2L of gel) by controlling the optimized operating parameters using the vortex reactor (VR)according to the procedure outlined in our previous work. 16In details, two different solutions, one of titanium tetraisopropoxide (TTIP; Sigma-Aldrich) in isopropyl alcohol and the other of water (Milli-Q)in isopropyl alcohol were prepared separately under a nitrogen ﬂux to control the alkoxide reactivity with humidity. Hydrochloric acid (HCl;Sigma Aldrich) was added to the second solution as a hydrolysis catalyst and deagglomeration agent. A TTIP/isopropylalcohol concentration was taken as 1 M/Lto obtain the maximum TiO 2yield (1M), W ([H2O]/[TTIP])
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† Politecnico di Torino.
‡ COMSATS Institute of Information Technology Lahore Campus.
Ind. Eng. Chem. Res. XXXX, xxx, 000A 10.1021/ie1005756 XXXX American Chemical Society