Study the influence of silver and cobalt on the photocatalytic activity of copper oxide nanoparticles for the degradation of methyl orange and real wastewater dyes

CuO (S1) Single pure component nanoparticles (SPCNPs), Ag/CuO (S2) binary component hybrid nanoparticles (BCHNPS), Co1/Ag/CuO (S3), and Co2/Ag/CuO (S4) ternary component hybrid nanoparticles (TCHNPS) were synthesized via co-precipitation method. Several spectroscopic methods investigated the characterization of the prepared catalysts. Based on Crystal properties, CuO exhibit a monoclinic phase (tenorite); the grain size of the prepared samples was 28.15 nm, 29.42 nm, 27.86 nm, and 26.67 nm for S1, S2, S3, and S4 respectively. The addition of different content from Co as a dopant to silver decorated CuO gives a clear change to a flake shape. The presence of the IR absorption peaks in the region 400–600 cm−1 matched to the distinctive stretching vibrations of Cu–O bonds in the monoclinic phase structure of CuO. Disappearance of the Raman peaks of CuO and appearing of the new characteristic peaks of cobalt oxide confirms the doping process. Using DRS analysis, arrange of the bandgap values were S1 > S2 > S3 > S4. For the synthetic methyl orange and raw industrial dye, the photodegradation parameters were measured. The results show the excellent activity of Co2/Ag/CuO NPS compared with other samples. Electrical studies of the catalysts show a higher value for the dielectric constant in the higher and lower frequency regions for the sample S4. The hopping process of the charge carrier’s improving as a result of the increase of applied field frequency which leads to an increase in the material conductivity.


Introduction
In past decades, parallel with the increase in population and the huge development in industrial and technological activities, the world suffers from many environmental problems. This growth has resulted in the formation of large contents of hazard compounds [1]. Many of these compounds are toxic, mutagenic and carcinogenic and may pose a threat to human life and environment [2][3][4]. One of the most important of the environmental problems is water pollution. Water pollution is a term referred to the presence of an excess of hazardous substances or heat that is harmful to the desirable life of humans, animals and living communities in or near water bodies. Frequently, Water pollution has a binary problem for industrial activities. It is important for the plant to condition the water before use, as well as to treat the wastewater use pretreatment of the water becomes necessary to avoid a number of problems such as existence of organic matter as a contaminate causes taste and odors, often adsorbed by various processes, forms colored colloidal suspensions [5][6][7]. One of the most common and dangerous pollutants found in water is organic pollutants. Some organic pollutants, even with low amounts, can cause many diseases that affect human life. Unfortunately, organic substances remain in the environment for a long time. Industrial dyes, especially textile dyes, represent a major source of organic water pollutants, which leads to numerous environmental risks [8][9][10]. The presence of these colored organic dyes in the environment is the main source of water pollution it can create many hazardous compounds through processes such as oxidation or hydrolysis and other chemical reactions. Therefore, there is increasing interest in the treatment and degradation of these dyes and their transformation into non-toxic compounds. Heterogeneous advanced oxidation technology (HET.AOT) is one of the new methods widely used for the decomposition or decolorization of the organic dyes [9,[11][12][13]. Semiconductor metal oxide nanoparticles are a very important member of the family of (HET.AOT). The strategy of the process mainly depends on the movement of electrons from the valence band (VB) to the conduction band (CB) on a surface of the semiconductor metal oxide nanoparticles by illumination with a suitable wavelength of light. These created excitons react with oxygen or water to produce superoxide anions and hydroxyl radicals as a reactive oxygen species (ROS) [14,15]. These species possess the great oxidizing potential to destruct several types of materials including industrial organic dyes. P-type semiconductor CuO NPs as a selective photocatalyst has attained a high degree of interest owing to their large uses in different areas because of low formation cost, superior stability, high electrical and optical properties. Surface morphology and crystal nature of CuO nanoparticles play a remarkable function in their properties [16]. To modify the properties of nanoparticles is the introduction of dopant materials in the lattice of original system. Due to promising environmental compatibility, large bandwidth, high photosensitivity, and chemical stability, addition of Silver (Ag) enhance the photocatalytic ability of semiconductor metal oxide NPs [17]. This improvement occurred by broadening UV-vis absorption, production of surface oxygen vacancies, and preventing the reformation process of charge centers. Compared with binary components hybrid nanoparticles (BCHNPs), ternary component hybrid nanoparticles (TCHNPs) have been extensively studied. The reaction between different components in the ternary hybrid compounds can greatly promote the activity of a nanocomposite system. The superior properties give a prominent work in catalytic, electronic, magnetic, and optical fields for the several environmental applications of TCHNPS. Cobalt incorporated TCHNPs have attracted major attention due to their great adsorption capacity, high surface area, good stability, high catalytic ability and environmentally friendly characteristics [18][19][20]. Also, presence of cobalt increases the number of defects on the serfuce of CuO NPs. This leads to an increase in the time of recombination process. According to the previous information, in this work, Co-doped CuO decorated by Ag nanoparticles was prepared using co-precipitation method and evaluated their photocatalytic performance. We present here a simple co precipitation method for senthysizing a new heterostructure catalyst Co-doped CuO decorated by Ag nanoparticles as the optimale component for enhance the photocatalystic properties of CuO NPs to increase the efficiency of the degradation of the synthetic and real organic dyes as a water pollutants. The prepared photocatalysts were analyzed using XRD, DRS, SEM, FT-IR, and Raman spectra. The role of Ag and Co in the binary and ternary component hybrid nanoparticles to photodegradation process of methyl orange (MO) and industrial raw dye under xenon light source was investigated. The photodegradation efficiency %, the rate constant (K), half lifetime (T 0.5 ), Percent of total organic carbon (TOC %) and removal percent of chemical oxygen demand (COD %) were measured. Photocatalytic estimation of the samples under different light sources showing the prepared Co2/Ag/CuO NPs give a promising superior sample in the photodegradation process. For the electrocatalyst samples, Dielectric properties and electrical conductivity were measured as a function of frequency.

Preparation of photocatalysts 2.2.1. Preparation of SPCNPs (CuO)
Initially, nitrate salt of copper (1 M) dissolve in deionized water (100 ml) was prepared with stirring for 15 min 1.5 M of Sodium hydroxide solution as a reducing agent slowly added to a Copper solution with vigorous stirring for 120 min at 333 K to produce a light blue precipitate of copper hydroxide. After that, the formed precipitate was filtered and washed by deionized water and absolute ethanol for many times and preserved at 373 K for 12 h in a hot air oven. The product was ground more times and calcined for 3 h at 1073 K to produce a final powder CuO NPs (S1).

Preparation of BCHNPs (Ag/CuO)
Ag-decorated CuO NPs (S2) was fabricated using the same precipitation method used to preparation of pure CuO NPs. In the excellent experimental procedures, 10 ml (1 M) of silver nitrate was added to 90 ml (1 M) copper nitrate tetrahydrate. Subsequently, drop wisely Sodium hydroxide was added to the previous solution at 333 K with stirring for 2 h. The same conditions from the filtration, washing, drying, and calcination used in preparation of CuO NPs were applied to the formation of second sample Ag/CuO NPS.

Preparation of TCHNPs (Co/Ag/CuO)
Using the same procedures and conditions in the two previous preparations, ternary component hybrid nanoparticles Co/Ag/CuO NPs with different cobalt content were prepared by addition of 5 ml and 10 ml of (1 M) cobalt Nitrate solution to the solutions of (85 ml copper solution +10 ml silver solution) and (80 ml copper solution +10 ml silver solution) to preparation of Co1/Ag/CuO NPs and Co2/Ag/CuO NPS respectively. The growth mechanism for the preparation of the catalysts have been explained as follows:

Characterization techniques
The prepared photocatalysts were characterized by the following analysis: the crystal structure was investigated by x-ray powder diffraction (X-600 Shimadzu-Japan) at 30 mA and 40 kV for the target Cu Kα with λ=0.154 nm. Images taken from a scanning electron microscope (model-JSM 6360 LA, Japan) used to study the morphological structure of the catalysts. In the range of 400-4000 cm −1 , Thermo Scientific Nicolet iS50 FTIR spectrometer used to examine the characteristic vibrational modes of the prepared samples. Thermo Scientific, DXR FT-RAMAN attached with a microscope used at room temperature for recording Raman scattering spectra. UV-Vis-NIR spectrophotometer (UV-3600) was employed to measure the ultraviolet-visible absorption spectra of the nanoparticle samples. Dielectric properties and electrical conductivity measured at room temperature during the frequency range from 1 kHz to 10 MHz by Semiconductor Characterization System (Keithley type-4200-SCS).

Assessment of photocatalytic performance
Prepared photocatalyst samples CuO NPs, Ag/CuO and Co1, 2/Ag/CuO were used under 50-watt Xenon lamp as a light source (Engineering company, Egypt) to reach the best conditions necessary for the photodegradation of methyl orange as a selected synthetic and raw organic dye which was taken from the station of industrial wastewater treatment, Cairo, Egypt. The photodegradation parameters include the type and content of the photocatalyst and irradiation time. The chosen concentration of methyl orange dye is (2×10 −5 M). The processing pathway can be started by addition of prepared photocatalyst (100 mg) into 100 ml of the organic dye. For one hour, the formed suspension solution was stirred to the complete equilibrium between adsorptiondesorption process and, therefore, the solution is ready for exposure to the light source. UV-vis spectrophotometer (Shimadzu) used to measure the absorbance changes of the methyl orange dye at a maximum wavelength (464 nm) with interval times (20 min for each run) for 120 min.
Where R % is the rate percent while Co and Ct are the concentration of dye, TOC and COD value before and after irradiation.

Results and discussion
3.1. Structural characteristics X-Ray Diffraction patterns of the prepared samples were presented in figure 1. In the single metal oxide CuO NPs, it was observed a well matching between the diffraction peaks and JCPDS data card no. 05-0661. XRD analysis detects that CuO emerges several fully-defined peaks of monoclinic phase (tenorite) CuO. In figure 1 Where D, λ, β and θ are the crystallite size, the wavelength for the target Cu Kα (0.154 nm), the width of a line shape at half of its maximum amplitude (FWHM) and the diffraction angle. In the presence of silver the crystallite size increase from 28.19 nm to 29.78 nm as a result of the highly ionic radius of Ag (0.129 nm) [28] compared with Cu (0.087 nm). With the increase in the dopant Co contents the crystallite size decreases according to the lowering ionic radius of Co (0.079 nm) table 1.
The active surface area of the particles S in m 2 g −1 was studied by the equation: Where D is the crystallite size in nm evaluated from the (−111) diffraction plain, XRD data (figure 1), and ρ is the CuO density (6.49 g cm −3 ). This equation is acquired, as debated in [29]. To determine the degree of disorders inside the matrix crystal, the dislocation density (δ), was estimated from the equation: According to the Williamson-Hall relation [30], the micro-strain (ε) in the crystal structure was estimated by: The dislocation density (δ) and the crystal lattice micro-strain (ε) were established to be decreases as a result of the presence of Ag as a decorated surface layer on the CuO nanoparticles figure 2. Also the doping of Co in the lattice of the CuO leads to an increase in the dislocation density (δ) values and a decrease in the lattice microstrain (ε). The decrease in values of δ and ε is due to the apparent variation between the ionic radiuses of added atoms compared with the matrix atom. The morphology structure of the prepared samples shows that the particles are agglomerated, and nanoparticle size is not regular. The larger nanoparticles may be ascribed to agglomeration of small particles, and the individual nanoparticle shapes distinctly invisible due to the agglomeration process.

FT-IR studies
FT-IR analysis is a significant method used to determine supplementary features of the prepared nano photocatalysts by identification of their characteristic peaks, as presented in figure 4. For the sample S1, the presence of the absorption peaks in the region 400-600 cm −1 matched to the distinctive stretching vibrations of M-O bonds in the monoclinic phase structure of CuO [31]. The peak located at 863 cm −1 corresponds clearly with Cu-O-H vibration. The appearing of the peak at 963 cm −1 is due to C−H out of plane deformation [32].
The reason for absorption peak at 1436 cm −1 is attributed to the presence CH 3 asymmetric stretching on the surface of CuO NPs. The existence of CO 2 in air was assigned by appearing of the peak at 2070 cm −1 [33][34][35].
Bending vibration of H-O-H and stretching vibration of O-H was assigned to the peaks at 1683 cm −1 and 3317 cm −1, respectively [36]. By the addition of Ag then Co in the samples S2, S3, and S4, a little shift was observed in the main absorption peaks of CuO NPs. This confirms that there is no chemical interaction between the copper oxide and the added elements or a slight occurrence. The minor shift towards the low frequency can be correlated with the bond length variation.

Raman studies
Raman analysis gives us information about phase-type, crystal structure and energy dispersion of nanoparticle compounds. Generally, the study of Raman spectra for the nanomaterial's is depending on the phonon confinement pattern (PCP), which highly affected by the grain size and shape. Figure 5 represents the Raman spectrum of the nanoprepared samples. Using group theory, CuO possesses 12 zone centers at the point Γ of the Brillouin zone (BZ), (Au+2Bu) are acoustic modes, (3Au+3Bg) are infrared modes and (Ag+2Bg) are the modes of Raman active [37]. Due to the symmetry of the site in copper oxide, the displacement of oxygen atoms contributes to the three active modes, while the atoms of Cu remain constant and ineffective for the Raman modes. The first mode (Ag) located at 286 cm −1 is due to in-phase /out phase rotation [38]. The second and third modes are associated with B1g at 333 cm −1 , and B2g at 617 cm −1 are attributed to bending of CuO, and the symmetric stretching of oxygen, respectively [39,40].   Disappearing the characteristic peaks of CuO and appearing of the new peaks is due the complete substitution process between copper and cobalt in the lattice and thus, the doping process is confirmed.

Optical studies
As one of the nondestructive techniques, diffused reflectance spectroscopy (DRS) used to characterize the optical parameters of nano-composite materials. Specifically, it is considered the best technique to evaluate optical characteristics of semiconductor materials. DRS spectrum for powder nanostructures from undoped and co-doped CuO with infinite thickness was evaluated and indicated in figure 6(a). By using Kubelka-Munk model the prepared photocatalysts band gap was estimated from DRS data. From the curve between (F(R) hυ) 2 and hυ the optical band gap is evaluated according to Kubelka-Munk and Tauc's equations as given below [42,43]; Where R, hυ, h, and n are the reflectance, energy of a photon, constant of plank, and a transition nature dependent value, respectively. The optical band gap was estimated from the x-axis at the intercept with the straight line. The bandgap energy values for prepared nanoparticles S1, S2, S3, and S4 are 3.47, 3.46, 3.44 and 3.40 eV, respectively. The estimated values of the optical band gap were listed in table 1 as indicated in figure 6(b). Increasing Co content in the photocatalysts decreases the optical band gap which leads to absorption edge redshift. A decreasing in the optical band gap energy could be ascribed to the increase in density of vacancies by oxygen and disorders according to the ionic radius differences between the Cu and Co ions as a result of the substitution process. The decrease in values of the energy of the bandgap could be attributed to quantum confinement effect. As a result of the light absorption in the nanomaterial semiconductors the valance band electrons transport to a particular position in a conduction band to produce electron hole-pair in the two bands respectively, when the nanoparticle size is identical to the wavelength of de Broglie the conduction band considers as a quantum hole for the electrons. Dagher et al have evaluated the bandgap of CuO NPs with  [44][45][46]. From these results we can conclude that the optical band gap of the semiconductor nanoparticles might be changed by nano-composites formation procedures.

Photocatalytic performance
The photocatalytic efficiency of the prepared samples pure CuO NPs (S1), Ag/CuO (S2), Co1/Ag/CuO (S3), and Co2/Ag/CuO (S4) were estimated using the destruction of methyl orange (MO) dye solution under xenon light irradiation. The decomposition process can be detected by measuring the difference in the intensity of the maximum peak of the methyl orange dye (λmax.464 nm). Figures 7(a)-(d) displays the absorption spectra of the dye in the presence of nano prepared samples at the time intervals of 20 min for 120 min as a selected time of irradiation process. At irradiation time, the reduction of the concentration of MO dye was (39%), (51%), (75%) and (87%) in the presence of (S1), (S2), (S3) and (S4), respectively. Figures 8, 9 present the influence of the photocatalysts on the absorbance value at different interval times (20 min for each test) and photodegradation performance of the organic dye, respectively. The first-order kinetic rate constants for the samples give  of the samples from 3.47 eV, 3.46 eV and 3.44 eV for pure CuO NPs (S1), Ag/CuO (S2) and Co1/Ag/CuO (S3), respectively to 3.40 eV in case of Co2/Ag/CuO NPs (S4) and thereby, the absorption process extends to the wider range in the visible light region, which promotes the photodecomposition process. Also, the reduction of energy band gap leads to the increase of the time required to recombination of electron-hole pairs and improve the production of O 2 and OH radicals as a reactive oxygen species (ROS), which are responsible for the decomposition of the organic dye into CO 2 and H 2 O. With previous effect of lowering energy bandgap, the crystal properties of the samples confirmed that the sample Co2/Ag/CuO NPs have high crystallinity, smaller crystallite size, and high active surface area compared with other prepared photocatalysts. All of the above properties improve the absorption of the sample (S4) to the light and thus increase its efficiency in the photodestruction process. Furthermore, SEM images figure 3 display the agglomeration particles in the (S4) sample; this indicated the reduction of the surface area and highly photocatalytic efficiency of prepared nanopowder that contain higher concentrations of cobalt in the photodegradation process. By the comparison with reported values, the results in the present work are comparable or even better in some cases [47][48][49][50][51].

Effect of pH
The Photodegradation of methyl orange dye in the presence of Co2/Ag/CuO photocatalyst at different pH values within the range of 3-11 was studied and presented in figure 11. The concentrations used for the organic dye and catalyst in this test are the same as in experiments of photodegradation process. From the  obtained results, the superior efficiency is occurred at pH7 (neutral medium) while there is a decrease in the degradation rate in the acidic and alkaline medium and be more clear at pHs 3and 11 respectively. At pH 3 (highest acidic medium), the lowering in the photodegradation activity is attributed to electrostatic repulsion between cationic organic dye and the catalyst used. On the other hand, at pH 11(highest alkaline medium), The large decrease in the number of active sites on the surface of the catalyst resulting from strong adsorption of the dye leads to inhibition of the decomposition process.   Figure 11. Effect of pH on the degradation of MO dye in the presence of Co2/Ag/CuO catalyst . Figure 12 shows the effect of different light sources on the COD removal percent for the methyl orange solution (2×10 −5 M) for 120 min as an irradiation time. Using the optimum photocatalyst sample (S4), the recorded values of COD removal were 91%, 71%and 62% under xenon lamp light, ultraviolet lamplight, and sunlight irradiation, respectively table 3. The lower activity with sunlight as a light source was attributed to the fact that UV represents only 3% of total solar energy [52]. The super activity in the presence of xenon lamp as a light source is attributed to many of its properties such as, high stability, long life, ability to emit a broad spectrum from UV to IR (185-2000 nm) and promote of photon energy for the activation of the prepared samples.

COD remaining of real wastewater under different light sources
In the presence of differently prepared photocatalyst (S1), (S2), (S3) and (S4) samples under different light sources for 120 min as an irradiation time figure 13, COD removal of dyes and other organic pollutants in the real effluent was studied and used to evaluate catalytic activity in the treatment of industrial wastewater, and values obtained are listed in table 4. Co2/Ag/CuO photocatalyst sample (S4) showed higher significant activity in the decomposition of dyes and organic pollutants in the wastewater. Using (S4) sample, the values of COD (ppm) reduced from 3510 to 724, 1125 and 1330 under xenon lamp, ultraviolet lamp, and sunlight irradiation, respectively. From the results, the photochemical detoxification process gives COD (ppm) lower than environment allowed save limit according to Egyptian Environmental Law (1000 ppm) under xenon lamp only [53,54]. While the photodegradation processes under ultraviolet lamp and sunlight light sources had COD values more than the allowed limit.
3.6.4. Photocatalytic activity mechanism for destruction of MO dye The photodegradation mechanism for methyl orange dye using CuO NPs, Ag/CuO and Co1,2/Ag/CuO under xenon lamp as a light source can be suggested in two stages, as shown in figure 14. The first stage is carried out by addition of Ag to the lattice of CuO NPs. When the CuO NPs is irradiated by xenon lamp, the electrons of valence band (VB) are excited and transfer to the levels of conduction band (CB) and at the same time, equal number of positive holes are formed at the level of valence band and thus silver contributes to the lack of the reformation process between negative electrons and positive holes. After that, silver reacts with oxygen to give  reactive oxygen radicals ( • O 2 −), and meanwhile, the hydroxyl radical ( • OH) can be created via the reaction between positive holes and water molecules. Both of the generated reactive species could interact with the organic pollutant to produce an effective photodegradation process. The second stage shows the effect of cobalt added on the photocatalytic performance of the samples. The presence of cobalt as a dopant leads to substitution between cobalt and copper in the lattice of Ag/CuO NPs. The replacement behavior is attributed to the symmetrical atomic size of both cobalt (0.087 nm) and copper (0.079 nm) [55]. In these conditions, a conduction band of CuO produces fresh impurity levels, which possess the ability to receive the electrons   Where c, d, and A are the sample capacitance and its thickness and area, respectively. Figures 15(a), (b) Indicated the effect of frequency on the dielectric parameters at room temperature during the frequency range from 1 kHz to 10 MHz. It is shown in figure 15(a) that, as the applied electric field frequency increases the dielectric constant (ε′) decreases by a low rate in the case of samples S1, S2 and S3. For the sample with higher content of cobalt S4, a sharp decrease was observed. According to Maxwell-Wagner effect, this states that the charge carriers are accumulated at the interface between the components in the lattice of the metal oxide nanoparticles with different relaxation time [56][57][58]. At the lower frequency the dielectric constant higher values of the studied samples mainly ascribed to the dipolar and space charge separations. The dielectric property of the material during the low-frequency region fully dependent on its permanent dipoles which aligns with the external applied electric field frequency. At the higher frequency region the electronic and ionic polarization present in the nanocomposite is the main reason for dielectric response. The dielectric constant (ε′) values at the higher and lower frequency regions are matched with Koop's theory [59]. Depending on the crystal structure of prepared samples, sample S2 with a larger crystallite size and lower number of grain boundary defects possess lower dielectric constant values. In the case of sample S4 with smaller crystallite size and larger number of grain boundary defects with a higher number of dipoles, the dielectric constant records higher values in the higher and lower frequency regions.

Dielectric loss (ε′)
The energy portion from the alternating electric field, which converted into heat in a dielectric medium is a dielectric loss. Figure 15(b) indicates that for the prepared co-doped CuO with lower amount of Co and undoped CuO the dielectric loss values are constant with the increase of frequency. This behavior may be ascribed to the larger grain size and lower number of grain boundary defects with the presence of space charge polarization in these samples.
On the other hand with the increase of the Co amount in the nano-composite, the initially dielectric loss increment with frequency in the lower region afterward it lowers with frequency in the higher region. This behavior might be due to a high and absolute responsibility of the electric dipoles under the effect of the applied electric field frequency [60][61][62]. Although of these factors above, the loss behavior of the dielectric with frequency appears to be so sophisticated and demands further investigations. Therefore, it can be terminated that the Co co-doped CuO nanomaterials can be used for the device applications at high frequency.

AC conductivity
The alternating conductivity s ac of the sample results from the charge carrier's motion during it is evaluated by the equation [63][64][65].
( ) s we e d =  ¢ tan 18 ac Where w, e  , e¢, and d tan are the angular frequency, the permittivity of vacuum, relative permittivity, and tangent delta. The ac conductivity versus frequency for the prepared nano-composites has been presented in figure 16. It was observed that during the lower frequency range the conductivity has a constant value with a flat shape. Actually, up to a frequency of 6 kHz, the values of σ ac were nearly the same for all the studied nanocomposites. However, at a higher range of frequency, a sharp increase was observed in the conductivity values. This may be ascribed to that; during these composites, an electronic interaction takes place, which increases electrical conductivity. Also, this occurs because as a result of the higher increase in the frequency accumulation process for the charge carriers' occurs at the grain boundaries. It was reported that the alternating conductivity related to the frequency and resulted from the polaron hopping mechanism of the charge carriers between the grain boundaries inside the material. The hopping process of the charge carrier's improving as a result of the increase of applied field frequency which leads to a raise in the material conductivity [66,67].

Conclusions
Using easy co-precipitation method, CuO NPs, Ag/CuO, and Co/Ag/CuO with two different concentrations of cobalt were successfully prepared and analyzed by various spectroscopic methods as XRD, SEM, DRS, FTIR and Raman spectra. Crystal structure confirms the monoclinic phase of CuO nanoparticles. The addition of different content from Co as a dopant to silver decorated CuO gives a clear change to a flake shape. The optical properties indicated that the presence of Ag then Co-doped CuO NPs gives a shift to the red region in the absorption band, thus leads to a reduction of energy band gap values. The formation of CuO NPs was assigned by the presence of the IR absorption peaks in the region 400-600 cm −1 . Appearing of the characteristic Raman modes of cobalt oxide0020confirms the doping process of cobalt in the lattice of copper oxide. The photodegradation of MO as a synthetic organic dye and industrial raw dye was studied after irradiation in the presence of prepared nanoparticle samples under xenon-lamp as a light source. The calculated rate percent of the degradation, COD removal for both investigated dyes demonstrates that the sample Co2/Ag/CuO possesses a highly photocatalytic activity compared with other samples under the same conditions. The values of dielectric constant and electrical conductivity of the prepared nanopowders indicate a higher electrical behavior of the sample with higher content of cobalt.

Acknowledgments
The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this workthrough research groups program under grant number R.G.P. 1/121/40.