Incorporated ZnO onto nano clinoptilolite particles as the active centers in the photodegradation of phenylhydrazine

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Abstract

ZnO was incorporated into nano particles of clinoptiloite by ion exchanging the zeolite in a zinc nitrate aqueous solution followed by calcinations process. All raw and modified samples were characterized by XRD, FT-IR, DRS, TG-DTG, SEM, BET and TEM. The prepared catalyst was used in the photocatalytic degradation of phenylhydrazine (PHZ) and the best experimental parameters were obtained as: 0.25 g L−1 of the catalyst, 20 ppm pollutant concentration and pH = 8. The degradation extent was monitored by UV–vis spectroscopy and the results were confirmed by HPLC and the chemical oxygen demand (COD).

Introduction

The hydrazine compounds are one of the most important environmental contaminants with different laboratory and industrial uses which can cause irreversible cellular damage due to their high toxicity [1]. Phenylhydrazine (PHZ) is one of the most potent carcinogens belongs to this family which used firstly as antipyretics, but the toxic action on red blood cells made their use dangerous. PHZ shows variety of toxic effects such as: inducing oxidative damage to hemoglobin [2], cancer [3], intoxication leads to hemolysis resulting in severe hemolytic anemia and reticulocytosis [4], and decreasing red blood [5]. Hence, the removing of this pollutant from industrial effluents is of great importance. Advanced oxidation processes (AOPs) are the most famous methods for removing different pollutants from water and wastewater by destroying most organic and some inorganic pollutants into CO2 and H2O [6]. In the heterogeneous photocatalysis, as famous AOP method, by exciting a semiconductor such as ZnO with UV or vis photons, electron–hole pairs and finally hydroxyl radicals will produce which destroy different pollutants in a nonselective process [7], [8], [9].

In addition of different applications of zinc oxide [8], [9], [10], due to its band gap of 3.37 eV (375 nm), it has widely used as a suitable semiconductor in the heterogeneous photocatalysis [11], [12], [13], [14], [15], [16], [17]. ZnO powder has higher quantum efficiency with respect to TiO2 and also high surface reactivity due to its large number of active surface defects. In addition, it can absorb a large fraction of solar spectrum. Hence it shows the higher reaction and mineralization rates [18], [19], [20], [21]. Despite the advantages of semiconductors, poor adsorption capacities of them limit their application. Doping of semiconductors onto a suitable support overcomes this limitation due to: increasing in charge separation, an increased lifetime of the charge carriers, and an enhanced interfacial charge transfer to adsorbed substrates [22], [23]. Among the various supports, zeolites are the famous candidates due to their high surface area, high adsorption capacity and high ion-exchange capacity [6], [24]. Moreover, their inorganic framework preserves them from photo-decay.

Although, phenol and different phenolic derivatives such as: nitro and chlorophenols, have been studied in various photodegradation and removal experiments [24], [25], [26], [27], [28], [29], [30], [31], [32], but, as far as we know based on our search, there no any papers toward the photodegradation of phenylhydrazine. Hence, we prompted to use it as a pollutant in the proposed photodagradation experiment. The aim of this work is increasing the photocatalytic efficiency of ZnO by supporting onto nanoparticles of clinoptilolite during ion exchange and calcinations processes. The obtained catalyst was used in the photodegradation of phenylhydrazine (PHZ) and the effects of some operating factors such as: catalyst mass, concentration of the pollutant and pH of the solution were investigated on the efficiency of the process.

Section snippets

Materials

The natural clinoptilolite tuffs (CP) belong to Semnan region in the north-east of Iran and purchased from Afrand Touska Company (Isfahan, Iran). Zn(NO3)2·5H2O, TiO2, phenylhydrazine (PHZ) and other used analytical grade chemicals were purchased from Aldrich or Merck. Distilled water was used throughout the experiments. The pH of solutions was appropriately adjusted with sodium hydroxide or hydrochloric acid solution.

Preparation of nano-clinoptilolite powder

Natural clinoptilolite tuffs were mechanically pretreated, by crushing in an

FT-IR results

FT-IR spectra of the NCP, Zn–NCP and ZnO–NCP particles are shown in Fig. 1. In all spectra, the located peak at about 1640 cm−1 belongs to vibration mode of the adsorbed water on the surface of the samples. The strongest absorption peak about 1074 cm−1 relates to the framework stretching vibration band of Si(Al)–O of zeolite which does not shift during the ion exchange and calcination (at 450 °C) processes indicating the high stability of zeolite structure. However, a broad absorption band in the

Conclusion

The results of this work confirm that the supported ZnO onto the surface of micro and nano sized clinoptiloite has much photocatalytic efficiency toward phenylhydrazine with respect to unsupported ZnO. On the other hand, zeolite prevents from aggregation of ZnO particles and hence improves the photocatalytic activity. In addition, the nano sized zeolite improves the photodegradation efficiency of ZnO particles with respect to the micro sized zeolite due to the increased surface area. Obtained

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