Synthesis and Photocatalytic Activity Investigation of CuO Nanorod Functionalized with Porphyrin

In this work, a simple wet-chemical method was used for preparing of CuO nanorods in the presence of a nonionic surfactant, polyethylene glycol. Furthermore, CuO functionalized with porphyrin was synthesized for first time. The synthesized photocatalysts were characterized by IR, XRD, and SEM analysis. The photocatalytic activity of the synthesized catalysts were investigated in degradation of methylene blue under visible light irradiation.


Introduction
About 15% of the total world production of dyes is lost during the dyeing process and is released in the textile effluents. The release of those colored waste waters in the ecosystem is a dramatic source of non-aesthetic pollution, eutrophication and perturbations in the aquatic life. As international environmental standards are becoming more stringent (ISO 14001, October 1996), technological systems for the removal of organic pollutants, such as dyes have been recently developed. Among them, physical methods, such as adsorption, biological methods (biodegradation) and chemical methods (chlorination, ozonation) are the most frequently used [1].
There is a growing interest in the field of nanostructured materials in recent years due to their enormous applications in opto-electronic devices, solar cells, catalysis, sensors, drug design etc.
Nanostructured materials are also employed in water treatment, such as removal of hazardous dyes and other toxic organic compounds and metals from water. Various biomass and waste materials are used to remove hazardous dyes, metals and other toxic contaminants from water. These processes are further improved by the introduction of nanostructured materials instead of waste products and biomass [2].
Dye sensitization is considered to be an efficient method to modify the photoresponse properties of CuO nanorod. Metal porphyrin may be an appropriate candidate because of its high absorption coefficient within the solar spectrum and its good chemical stability in comparison to that of other dyes [3].
In the past few years, CuO has attracted increasing interest for both fundamental and practical reasons. It has been shown that CuO is an important industrial material that can be widely used in applications such as gas sensors, magnetic storage media, solar-energy transformation, electronics, semiconductors, and catalysis. CuO is a p-type semiconductor. The direct band gap energy of CuO nanorods is evaluated to be 2.75 eV (450.85161nm). Recently, the synthesis of one-dimensional nanostructural materials such as nanorods or nanowires of various materials has received considerable attention, and the potential wide-ranging applications of these nanostructural materials have been predicted. For the preparation of nanorods or nanowires of desired materials, many methods have been developed including arc discharge laser ablation, templates, and other methods. However, high temperatures, special conditions, tedious procedures, or complex apparatus may be required for these methods. Here we report a simple wet-chemical method for preparing CuO nanorods in the presence of a nonionic surfactant, polyethylene glycol (PEG; Mw 20 000). This method requires neither complex apparatus nor long synthesis times. CuO nanorods can be prepared easily and effectively without complicated control of the reaction conditions [4].
The chemistry of porphyrin derivatives has played an important role especially during the past decade in particular branches of new materials science, and many researchers have undertaken projects on the synthesis of variously substituted compounds to obtain new functional materials.
Porphyrin derivatives have been found to possess application for the construction of solar cells as light absorbents in organic dyes displaying notable stability and unique chemical, physical, and spectroscopic properties [5].
In our experiment, prepared CuO nanorods was photosensitized with TCPP to improving the visible spectral absorption and photoactivity under visible light irradiation. The photocatalytic properties of synthesized catalysts were investigated in photodegradation of methylene blue in the visible light irradiation. Moreover, the effect of porphyrin photosensitizer in improving of visible light photoactivity was discussed in details.

Preparation of CuO nanorods
All of the chemical reagents used in this experiment were of analytical grade. CuO nanorods were precipitate was heated by putting on a steam tracing for 30 min to ensure that the Cu(OH)2 was turned into CuO completely. The black CuO precipitate was washed with distilled water several times and then with EtOH to remove the PEG completely, filtered, and dried in an oven at 80 • C for 5h.

Photosensitization of CuO by TCPP
CuO and porphyrin were dissolved in DMF. The obtained solution refluxed at 150 o C. The product were separated by centerfiguration and washed with DMF.

Characterization of TCPP
The FT-IR spectrum of TCPP is illustrated in Fig. 1. The FT-IR spectra were recorded on a FT-IR spectrometer (4000 -400 cm -1 ) in KBr pellets; As shown in Fig. 1, FT-IR spectra of compound with the characteristic peak of C-H vibration of toluene in the range of 2920 cm -1 indicated that the relative schiff base porphyrin were successfully synthesized.

Morphological characterizations
The SEM images of the CuO nanorods are shown in Fig. 4. Typical SEM images of the CuO nanorods revealed that these materials have a relatively straight rod-like shape and smooth surfaces. It can also be seen that the nanorods are of uniform lengths of up to 400 nm.

Photocatalytic activity investigation
The photocatalytic activity of CuO photosensitized with porphyrin were evaluated by the degradation of MB dye (10 ppm) solution under visible light illumination. 2 mg of photocatalyst was dispersed in 20 ml of MB aqueous solution by sonication. The solution was then exposed to visible LED irradiation for 3h. The degradation was monitored by measuring the absorbance amount using a double beam UV-vis spectrophotometer (Shimadzu UV-1700). Based on the photodegradation results, the photoactivity of TCPP-CuO was about 4 times higher than that of the pure CuO (Fig. 5). To the best of our knowledge, this result represents the porphyrin ability in absorbing of visible light. In this photocatalyst, porphyrin acts as a visible light harvesting agents. CuO is a wide band gap semiconductor. Thus it can not absorb visible light well. In CuO photosensitized by TCPP, porphyrin can absorb wide range of visible light due to the high absorption coefficient in the UV-vis spectrum. Therefore, this photocatalyst are active in the visible light.

Conclusion
As a whole, in this work CuO nanorods were prepared using a simple wet-chemical method. The