Photocatalytic Dye Degradation and Biological Activities of Cu-Doped ZnSe Nanoparticles and Their Insights

: Environmental nanotechnology has received much attention owing to its implications on environmental ecosystem, and thus is promising for the elimination of toxic elements from the aquatic surface. This work focuses on Cu-doped ZnSe nanoparticles using the co-precipitation method. The synthesized Cu-doped ZnSe nanoparticles were examined for structural, optical, and morphological properties with the help of XRD, FTIR, UV/vis diffuse reﬂection spectroscopy (DRS), FESEM, TEM, and XPS. The synthesized Cu-doped ZnSe nanoparticles revealed the presence of Cu 2+ in the ZnSe lattice, which has been shown to take a predominant role for enhanced catalysis in the Cu-doped ZnSe nanoparticles. The synthesized Cu-doped ZnSe nanoparticles were investigated for their catalytic and antibacterial activities. The 0.1 M copper-doped ZnSe nanoparticles exhibited the highest rate of degradation against the methyl orange dye, which was found to be 87%. A pseudo-ﬁrst-order kinetics was followed by Cu-doped ZnSe nanoparticles with a rate constant of 0.1334 min − 1 . The gram-positive and gram-negative bacteria were used for investigating the anti-bacterial activity of the Cu-doped ZnSe nanoparticles. The Cu-doped ZnSe nanoparticles exhibited enhanced photocatalytic and antibacterial activity. Cu-doped ZnSe. The phase purity, optical transformations, and valency of the Cu-doped ZnSe nanoparticles revealed the structural modiﬁcation of the catalyst. Different concentrations of Cu-doped ZnSe nanoparticles were used to study the catalytic activity. Among them, 0.1 M Cu-doped ZnSe nanoparticles have exhibited excellent photocatalytic activity towards MO dye. The 0.1 M Cu-doped ZnSe nanoparticles also exhibit noticeable antibacterial activity against the gram-positive and gram-negative bacteria. This work suggests that the Cu-doped ZnSe nanoparticles portray a prominent photocatalytic and antibacterial activity. Hence, the synthesized Cu-doped ZnSe nanoparticles can be used for developing a large-scale wastewater puriﬁcation system for the degradation of contaminates.

Researchers have taken an immense interest in employing nanoparticles for photocatalytic dye degradation. The photocatalytic degradation process [8,9] is a highly efficient oxidation method for decomposing organic contaminants. The electrons are excited and steered from the valence band to the conduction band of the photocatalyst using energy selenium powder (0.5 M) was added with sodium hydroxide solution to obtain the sodium hydroxide selenide solution. The zinc and selenium solution was then heated to 100 • C while maintaining the pH at 10 with NaOH. The reaction mixture was then allowed to stir for 24 h at 100 • C. Thereafter, the obtained precipitate was washed with ethanol or distilled water followed by drying in vacuum for 48 h at 80 • C. Finally, the processed powdered sample was kept in an oven for 200 • C. The as prepared powder sample was then used for further measurements. The same method was used for synthesizing 0.05 M, 0.01, and 0.1 M copper nitrate-doped ZnSe nanoparticles [25]. The synthesis process of Cu-doped ZnSe nanoparticles is depicted in Scheme 1.
Water 2021, 13, x FOR PEER REVIEW 3 of 13 copper nitrate solutions by continuously stirring with a magnetic stirrer. Subsequently, selenium powder (0.5 M) was added with sodium hydroxide solution to obtain the sodium hydroxide selenide solution. The zinc and selenium solution was then heated to 100 °C while maintaining the pH at 10 with NaOH. The reaction mixture was then allowed to stir for 24 h at 100 °C . Thereafter, the obtained precipitate was washed with ethanol or distilled water followed by drying in vacuum for 48 h at 80 °C . Finally, the processed powdered sample was kept in an oven for 200 °C . The as prepared powder sample was then used for further measurements. The same method was used for synthesizing 0.05 M, 0.01, and 0.1 M copper nitrate-doped ZnSe nanoparticles [25]. The synthesis process of Cu-doped ZnSe nanoparticles is depicted in Scheme 1.

Scheme 1.
Synthesis steps of the Cu-doped ZnSe nanoparticles.

Antibacterial Activity
The bacterial evaluation of the synthesized Cu-doped ZnSe nanoparticles was analyzed using gram-positive (S. aureus) and gram-negative (E. coli) bacteria. The disc diffusion method was used to find the efficiency of the nanoparticles. Mueller Hinton broth was used to grow the bacteria overnight. The grown bacteria were isolated (100 μL × 10 −7 Scheme 1. Synthesis steps of the Cu-doped ZnSe nanoparticles.

Antibacterial Activity
The bacterial evaluation of the synthesized Cu-doped ZnSe nanoparticles was analyzed using gram-positive (S. aureus) and gram-negative (E. coli) bacteria. The disc diffusion method was used to find the efficiency of the nanoparticles. Mueller Hinton broth was used to grow the bacteria overnight. The grown bacteria were isolated (100 µL × 10 −7 CFU) and streaked onto the sterilized agar Petri plates. A paper disc was inserted onto the Petri plates with a diameter of 6 mm. The disc was loaded with various concentrations (25 µL, 50 µL, and 100 µL) of nanoparticles. The weighted discs were incubated for 24 h at 37 • C. The incubated discs were then probed for the zone of inhibition for the cultured bacteria. The zone shows prominent bacterial destruction, where the range of the zone was measured in mm scale [25]. The same experiment conditions were triplicated for accuracy.

Photocatalytic Dye Degradation
The photocatalytic dye degradation of MO dye was investigated by employing Cudoped ZnSe nanoparticles. The light source used for the experiment is a Xenon lamp that gives off visible light. The catalyst (10 mg) was dissolved in 100 mL of the dye solution and placed in dark conditions for 30 min. The dark condition helped to achieve the adsorption desorption equilibrium. Then, visible light was irradiated on the sample and, after a certain time interval, an aliquot of 3 mL from the solution was taken out and centrifuged at 5000 rpm to remove the nanoparticles to determine the dye degradation accuracy. The collected samples were recorded in a UV/vis spectrometer. The dye degradation efficiency was calculated using Equation (1) as follows: where C 0 denotes initial dye concentration without light and C is the light exposed dye concentration.

XRD Analysis
The XRD pattern of copper-doped ZnSe nanoparticles is shown in Figure 1. The copper peaks are indexed at 2θ = 43.8 • , 50.7 • , and 74.3 • , corresponding to (111), (200), and (220) miller planes, respectively. Their patterns are well-matched with the std. JCPDS card no. of 04-0836 with an FCC (face-centered cubic) structure [25,26]. The copper modifies the ZnSe nanoparticles, as shown in Figure 1. The ZnSe nanoparticles' peaks were observed at 2θ = 27.3 • , 45.3 • , 53.7 • , 66 • , and 73 • for (111), (220), (311), (400), and (203) planes, respectively. The distinct peaks of copper as introduced into the ZnSe nanoparticles by doping have marginally changed the nature of the ZnSe nanoparticles. By introducing copper into ZnSe, the cubic structure is modified with respect to the size and growth of orientation of the NP, which converts copper to Cu (II) phase. The Cu (II) phase is confirmed by the narrow XRD peaks at 31.7 • . The Cu (II) phase was reassured by the XPS technique. The pristine ZnSe nanoparticles are reoriented by the addition of copper into the crystal system. The copper-doped ZnSe nanoparticles' size was determined by the Debye-Sherrer equation. The calculated values are 18 < 24 < 31 nm for 0.01 < 0.05 < 0.1 M copper-doped into the ZnSe nanoparticles, respectively [27].
Water 2021, 13, x FOR PEER REVIEW 4 of 13 CFU) and streaked onto the sterilized agar Petri plates. A paper disc was inserted onto the Petri plates with a diameter of 6 mm. The disc was loaded with various concentrations (25 μL, 50 μL, and 100 μL) of nanoparticles. The weighted discs were incubated for 24 h at 37 °C. The incubated discs were then probed for the zone of inhibition for the cultured bacteria. The zone shows prominent bacterial destruction, where the range of the zone was measured in mm scale [25]. The same experiment conditions were triplicated for accuracy.

Photocatalytic Dye Degradation
The photocatalytic dye degradation of MO dye was investigated by employing Cudoped ZnSe nanoparticles. The light source used for the experiment is a Xenon lamp that gives off visible light. The catalyst (10 mg) was dissolved in 100 mL of the dye solution and placed in dark conditions for 30 min. The dark condition helped to achieve the adsorption desorption equilibrium. Then, visible light was irradiated on the sample and, after a certain time interval, an aliquot of 3 mL from the solution was taken out and centrifuged at 5000 rpm to remove the nanoparticles to determine the dye degradation accuracy. The collected samples were recorded in a UV/vis spectrometer. The dye degradation efficiency was calculated using Equation (1) as follows: where denotes initial dye concentration without light and C is the light exposed dye concentration.

XRD Analysis
The XRD pattern of copper-doped ZnSe nanoparticles is shown in Figure 1. The copper peaks are indexed at 2θ = 43.8°, 50.7°, and 74.3°, corresponding to (111), (200), and (220) miller planes, respectively. Their patterns are well-matched with the std. JCPDS card no. of 04-0836 with an FCC (face-centered cubic) structure [25,26]. The copper modifies the ZnSe nanoparticles, as shown in Figure 1. The ZnSe nanoparticles' peaks were observed at 2θ = 27.3°, 45.3°, 53.7°, 66°, and 73° for (111), (220), (311), (400), and (203) planes, respectively. The distinct peaks of copper as introduced into the ZnSe nanoparticles by doping have marginally changed the nature of the ZnSe nanoparticles. By introducing copper into ZnSe, the cubic structure is modified with respect to the size and growth of orientation of the NP, which converts copper to Cu (II) phase. The Cu (II) phase is confirmed by the narrow XRD peaks at 31.7°. The Cu (II) phase was reassured by the XPS technique. The pristine ZnSe nanoparticles are reoriented by the addition of copper into the crystal system. The copper-doped ZnSe nanoparticles' size was determined by the Debye-Sherrer equation. The calculated values are 18 < 24 < 31 nm for 0.01 < 0.05 < 0.1 M copper-doped into the ZnSe nanoparticles, respectively [27].

FTIR Analysis
The synthesized sample purity and surface modification of ZnSe nanoparticles doped with different Cu concentrations were evaluated by FTIR spectrum, as depicted in Figure 2. The different concentrations of Cu 2+ cations in ZnSe nanoparticles demonstrate different kinds of bond stretching and vibrations, as seen in the spectrum. Sample a contains a low intensity OH stretching bond. However, sample b and c show high intensity of the bond and a broad spectrum of OH stretching at~3500 cm −1 is observed. The peaks at 1593, 1622, and 1640 cm −1 indicate the interaction between the Cu 2+ , Zn 2+ , and Se 2− of the carboxylic acid group [28]. Bond frequencies at 1246, 1321, and 1305 cm −1 are responsible for the stretching vibration of the C-O group [29]. The peak intensities gradually increase when Cu 2+ cation concentration increased, boosting the interaction with the ZnSe nanoparticles. The increased peak values denote the reformation of the ZnSe nanoparticles when doped with Cu. The peaks at 488, 461, and 487 cm −1 are attributed to the presence of Zn-Se stretching vibrations, while those at 944, 940, 836, 834, 826, 720, 698, 692, 552, and 520 cm −1 correspond to the formation of Cu-Zn-Se by reduction of Cu 2+ [30]. The obtained peaks strongly indicate surface re-orientation of ZnSe nanoparticles and reduction of Cu 2+ and ZnSe nanoparticles [31]. The surface was strongly modified with the Cu addition/doping of the ZnSe nanoparticle in sample c. Sample c has a high-level interaction between the reactants and nano reduction of the synthesized samples occurred.

FTIR Analysis
The synthesized sample purity and surface modification of ZnSe n doped with different Cu concentrations were evaluated by FTIR spectrum, a Figure 2. The different concentrations of Cu 2+ cations in ZnSe nanoparticles different kinds of bond stretching and vibrations, as seen in the spectrum. S tains a low intensity OH stretching bond. However, sample b and c show h of the bond and a broad spectrum of OH stretching at ~3500 cm −1 is observe at 1593, 1622, and 1640 cm −1 indicate the interaction between the Cu 2+ , Zn 2+ , a carboxylic acid group [28]. Bond frequencies at 1246, 1321, and 1305 cm −1 ar for the stretching vibration of the C-O group [29]. The peak intensities gradu when Cu 2+ cation concentration increased, boosting the interaction with th particles. The increased peak values denote the reformation of the ZnSe n when doped with Cu. The peaks at 488, 461, and 487 cm −1 are attributed to th Zn-Se stretching vibrations, while those at 944, 940, 836, 834, 826, 720, 698, 520 cm −1 correspond to the formation of Cu-Zn-Se by reduction of Cu 2+ [30]. peaks strongly indicate surface re-orientation of ZnSe nanoparticles and redu and ZnSe nanoparticles [31]. The surface was strongly modified with t tion/doping of the ZnSe nanoparticle in sample c. Sample c has a high-lev between the reactants and nano reduction of the synthesized samples occurr  Figure 3a,b shows the synthesized Cu-doped ZnSe absorption and ban as measured by UV/DRS spectroscopy. The undoped ZnSe nanoparticles sho tion edge at 390 nm. However, when Cu was added to the systems, the ads shifted towards the lower wavelength side at 245 nm and broad-spectrum (sh at 650 nm) in the visible region [31]. The Cu 2+ ions to (Zn 2+ Se 2− ) ZnSe create sites at the surface. The blueshift occurred as a result of the introduction of The transfer of charge Cu 2+ /Zn 2+ → Se 2− has been shown to increase the optic The interaction between copper, zinc, and selenium shifted the optical ten lower side of the wavelength. In this case, the optical band gap is determine belka-Munk theory. The calculated band gap values are 2.65 eV, 2.43 eV, [25,32]. The narrow bandgap represents photocatalytic activity in the range o The energy gap between the pure ZnSe and doped ZnSe nanoparticle is ∆ which is redshifted. The decreased bandgap confirmed the formation of th [33]. The penetration/scattering ability is the main reason for the decreas These results suggest the potential application of the material for improved  Figure 3a,b shows the synthesized Cu-doped ZnSe absorption and bandgap energy as measured by UV/DRS spectroscopy. The undoped ZnSe nanoparticles show an absorption edge at 390 nm. However, when Cu was added to the systems, the adsorption edge shifted towards the lower wavelength side at 245 nm and broad-spectrum (shoulder peaks at 650 nm) in the visible region [31]. The Cu 2+ ions to (Zn 2+ Se 2− ) ZnSe create more active sites at the surface. The blueshift occurred as a result of the introduction of the Cu 2+ ions. The transfer of charge Cu 2+ /Zn 2+ → Se 2− has been shown to increase the optical behaviour. The interaction between copper, zinc, and selenium shifted the optical tendency to the lower side of the wavelength. In this case, the optical band gap is determined by the Kubelka-Munk theory. The calculated band gap values are 2.65 eV, 2.43 eV, and 2.06 eV [25,32]. The narrow bandgap represents photocatalytic activity in the range of visible light. The energy gap between the pure ZnSe and doped ZnSe nanoparticle is ∆Eg = 0.71 eV, which is redshifted. The decreased bandgap confirmed the formation of the active sites [33]. The penetration/scattering ability is the main reason for the decreased bandgap. These results suggest the potential application of the material for improved catalytic activity. Water 2021, 13, x FOR PEER REVIEW 6 of 13

FE-SEM and EDX Analysis
The surface morphology and elemental composition of the synthesized Cu-doped ZnSe nanoparticles were evaluated by field emission scanning electron microscope (FE-SEM) coupled with energy dispersive X-ray analysis (EDX), as shown in Figure 4a-f. The raw ZnSe nanoparticles have been shown to exhibit a spherical shape [32]. The presence of Cu 2+ ions in the ZnSe surface modifies the shape and size of the Cu-doped ZnSe nanoparticles (Figure 4a-c). The Cu-doped ZnSe nanoparticles exhibit a quasi-spherical shape. The modifications in the structure due to the dopant in various concentration (0.01, 0.05, and 0.1 M of Cu 2+ ions) induce a structural and morphological stability. The presence of low-level Cu 2+ in the ZnSe nanoparticles shows a mixed spherical shape (Figure 4a,b). The copper-rich ZnSe nanoparticle shows a better quasi-spherical shape than samples a and b (Figure 4c). The atomic and weight percentages of the elements present in the sample were measured by energy dispersive X-ray analysis (EDX) (Figure 4d-f). The presence of copper, zinc, and selenium confirms the existence of the respective elemental constituents. The elements and their atomic and weight percentages are tabulated in Figure 4d-f as an inset. The different concentration of Cu 2+ was listed in the EDX spectrum. The high copper content results in a change in the shape and size of the as synthesized nanoparticles.

FE-SEM and EDX Analysis
The surface morphology and elemental composition of the synthesized Cu-doped ZnSe nanoparticles were evaluated by field emission scanning electron microscope (FE-SEM) coupled with energy dispersive X-ray analysis (EDX), as shown in Figure 4a-f. The raw ZnSe nanoparticles have been shown to exhibit a spherical shape [32]. The presence of Cu 2+ ions in the ZnSe surface modifies the shape and size of the Cu-doped ZnSe nanoparticles (Figure 4a-c). The Cu-doped ZnSe nanoparticles exhibit a quasi-spherical shape. The modifications in the structure due to the dopant in various concentration (0.01, 0.05, and 0.1 M of Cu 2+ ions) induce a structural and morphological stability. The presence of low-level Cu 2+ in the ZnSe nanoparticles shows a mixed spherical shape (Figure 4a,b). The copper-rich ZnSe nanoparticle shows a better quasi-spherical shape than samples a and b (Figure 4c).

FE-SEM and EDX Analysis
The surface morphology and elemental composition of the synthesized Cu-doped ZnSe nanoparticles were evaluated by field emission scanning electron microscope (FE-SEM) coupled with energy dispersive X-ray analysis (EDX), as shown in Figure 4a-f. The raw ZnSe nanoparticles have been shown to exhibit a spherical shape [32]. The presence of Cu 2+ ions in the ZnSe surface modifies the shape and size of the Cu-doped ZnSe nanoparticles (Figure 4a-c). The Cu-doped ZnSe nanoparticles exhibit a quasi-spherical shape. The modifications in the structure due to the dopant in various concentration (0.01, 0.05, and 0.1 M of Cu 2+ ions) induce a structural and morphological stability. The presence of low-level Cu 2+ in the ZnSe nanoparticles shows a mixed spherical shape (Figure 4a,b). The copper-rich ZnSe nanoparticle shows a better quasi-spherical shape than samples a and b (Figure 4c). The atomic and weight percentages of the elements present in the sample were measured by energy dispersive X-ray analysis (EDX) (Figure 4d-f). The presence of copper, zinc, and selenium confirms the existence of the respective elemental constituents. The elements and their atomic and weight percentages are tabulated in Figure 4d-f as an inset. The different concentration of Cu 2+ was listed in the EDX spectrum. The high copper content results in a change in the shape and size of the as synthesized nanoparticles. The atomic and weight percentages of the elements present in the sample were measured by energy dispersive X-ray analysis (EDX) (Figure 4d-f). The presence of copper, zinc, and selenium confirms the existence of the respective elemental constituents. The elements and their atomic and weight percentages are tabulated in Figure 4d-f as an inset. The different concentration of Cu 2+ was listed in the EDX spectrum. The high copper content results in a change in the shape and size of the as synthesized nanoparticles.

HR-TEM Analysis
The synthesized Cu-doped ZnSe nanoparticles represent the HR-TEM image of quasispherical shape in Figure 5a,b. Cu 2+ ions have similar ionic radii to Zn 2+ ions in the Cu-doped ZnSe lattice. Therefore, the Cu 2+ ions are expected to be incorporated into the ZnSe crystal structure. The size of the Cu-doped ZnSe nanoparticle is 33 nm, which is nearly equal to the crystallite size. The poly crystallite nature of the spherical shape informed the formation of the Cu 2+ and Cu (II) phase in ZnSe nanoparticles. The raw ZnSe nanoparticle has been found to exhibit a spherical shape, but the presence of dopant as Cu reforms the shape into a quasi-spherical shape [25,34].
Water 2021, 13, x FOR PEER REVIEW

HR-TEM Analysis
The synthesized Cu-doped ZnSe nanoparticles represent the HR-TEM im quasi-spherical shape in Figure 5 (a & b). Cu 2+ ions have similar ionic radii to Zn 2+ the Cu-doped ZnSe lattice. Therefore, the Cu 2+ ions are expected to be incorporat the ZnSe crystal structure. The size of the Cu-doped ZnSe nanoparticle is 33 nm, w nearly equal to the crystallite size. The poly crystallite nature of the spherical sh formed the formation of the Cu 2+ and Cu (II) phase in ZnSe nanoparticles. The ra nanoparticle has been found to exhibit a spherical shape, but the presence of do Cu reforms the shape into a quasi-spherical shape [25,34].

XPS Analysis
The valency and chemical state and bonding between the materials were elu by X-ray photoelectron spectroscopy (XPS). Figure 6a-e represent the characterist trum of Cu-doped ZnSe nanoparticles in the survey spectrum (a), Cu-2p spectrum 2p spectrum (C), Se-3d spectrum (d), and C-1s spectrum (e). The Cu 2p3/2 (934.58 e Cu 2p1/2 (954.58 eV) (Figure 6a) represent the metallic Cu core with the differen eV (spin-orbit coupling). The remaining two peaks of the copper spectrum indicate 2p state and represent the existence of the Cu 2+ with a binding energy of 942.65 962.65 eV [35]. The peaks at 1022.23 eV and 1045.48 eV in Figure 6b point towards and Zn 2p3/2, respectively (Figure 6c) [36]. The selenium peaks at 59.33 eV and 5 represent Se-3d3/2 and Se 3d5/2, respectively [37]. The copper state of C-1s represe existence of Cu 2+ , Zn 2 + , and Se 2− in 285.40 eV (Figure 6e). The metal ions and b between them demonstrate the successful preparation of Cu-doped ZnSe nanop Copper is widely used for photocatalytic applications thanks to its oxidative ten The zinc selenide nanoparticles doped with copper metal result in enhancing the c activity used for degradation of the organic dyes and antibacterial activity.

XPS Analysis
The valency and chemical state and bonding between the materials were elucidated by X-ray photoelectron spectroscopy (XPS). Figure 6a-e represent the characteristic spectrum of Cu-doped ZnSe nanoparticles in the survey spectrum (a), Cu-2p spectrum (b), Zn-2p spectrum (C), Se-3d spectrum (d), and C-1s spectrum (e). The Cu 2p3/2 (934.58 eV) and Cu 2p1/2 (954.58 eV) (Figure 6a) represent the metallic Cu core with the difference of 20 eV (spin-orbit coupling). The remaining two peaks of the copper spectrum indicate the Cu 2p state and represent the existence of the Cu 2+ with a binding energy of 942.65 eV and 962.65 eV [35]. The peaks at 1022.23 eV and 1045.48 eV in Figure 6b point towards Zn 2p 1/2 and Zn 2p 3/2 , respectively (Figure 6c) [36]. The selenium peaks at 59.33 eV and 55.06 eV represent Se-3d 3/2 and Se 3d 5/2 , respectively [37]. The copper state of C-1s represents the existence of Cu 2+ , Zn 2 + , and Se 2− in 285.40 eV (Figure 6e). The metal ions and bonding between them demonstrate the successful preparation of Cu-doped ZnSe nanoparticles. Copper is widely used for photocatalytic applications thanks to its oxidative tendency. The zinc selenide nanoparticles doped with copper metal result in enhancing the catalytic activity used for degradation of the organic dyes and antibacterial activity.

Antibacterial Activity
The antibacterial activity of Cu-doped ZnSe nanoparticles was investigated by the dose diffusion method against gram-positive (S. aureus) and gram-negative (E. coli) bacteria. The Cu 2+ ions increased the zone of inhibition for the target species as the concentration of Cu-doped ZnSe nanoparticles increased from 25 µL to 100 µL. The three different concentrations of Cu-doped ZnSe nanoparticles were used to target the bacterial strains and develop a zone of inhibitions, as shown in Figure 7. The largest zone of inhibition is shown for the highest concentration of Cu. The dissolution rate and release of ions determined the destruction of the strains. Here, the gram-negative bacterial growth was suppressed more than that of gram-positive bacteria. The gram-negative bacteria cell wall is weaker than that of the gram-positive bacteria. Therefore, the Cu 2+ ions easily enter and constrict the growth of negative bacteria. Thus, the Cu-doped nanoparticles produce efficient antibacterial activity [38].

Antibacterial Activity
The antibacterial activity of Cu-doped ZnSe nanoparticles was investigated by the dose diffusion method against gram-positive (S. aureus) and gram-negative (E. coli) bacte ria. The Cu 2+ ions increased the zone of inhibition for the target species as the concentration of Cu-doped ZnSe nanoparticles increased from 25 μL to 100 μL. The three differen concentrations of Cu-doped ZnSe nanoparticles were used to target the bacterial strains and develop a zone of inhibitions, as shown in Figure 7. The largest zone of inhibition is shown for the highest concentration of Cu. The dissolution rate and release of ions determined the destruction of the strains. Here, the gram-negative bacterial growth was sup pressed more than that of gram-positive bacteria. The gram-negative bacteria cell wall is weaker than that of the gram-positive bacteria. Therefore, the Cu 2+ ions easily enter and constrict the growth of negative bacteria. Thus, the Cu-doped nanoparticles produce effi cient antibacterial activity [38].

Antibacterial Activity
The antibacterial activity of Cu-doped ZnSe nanoparticles was investigated by dose diffusion method against gram-positive (S. aureus) and gram-negative (E. coli) ba ria. The Cu 2+ ions increased the zone of inhibition for the target species as the concen tion of Cu-doped ZnSe nanoparticles increased from 25 μL to 100 μL. The three diffe concentrations of Cu-doped ZnSe nanoparticles were used to target the bacterial str and develop a zone of inhibitions, as shown in Figure 7. The largest zone of inhibitio shown for the highest concentration of Cu. The dissolution rate and release of ions d mined the destruction of the strains. Here, the gram-negative bacterial growth was pressed more than that of gram-positive bacteria. The gram-negative bacteria cell w weaker than that of the gram-positive bacteria. Therefore, the Cu 2+ ions easily enter constrict the growth of negative bacteria. Thus, the Cu-doped nanoparticles produce cient antibacterial activity [38].

Mechanism of Antibacterial Activity of Cu-Doped ZnSe Nanoparticles
The possible mechanism of Cu-doped ZnSe nanoparticles against bacteria is shown in Figure 8. The mechanism is based on two important actions, which are The positively charged nanoparticles target the negatively charge ing by the electrostatic force of attraction. The interaction results in ele tion, restricts DNA production, and damages the protein. The ROS f the multiplication/production of the bacteria, which leads to cell deat

Photocatalytic Dye Degradation
The photocatalytic dye degradation of Cu-doped ZnSe nanopart against the MO dye under a visible light source using a xenon lamp degradation spectrum is shown in Figure 9. The MO dye absorbance addition of a catalyst and increased time interval. The degradation ZnSe nanoparticles shows a decrease in absorbance by 75% for MO i dye is slowly shown to lose its colour with increasing time. The presen doped ZnSe nanoparticles enhances the surface area and induces pho degrade MO dye, as depicted in Figure 10a,b. The % of photodegra estimated as 78% < 83% < 87% for different concentrations of Cu in The photolysis process without the catalyst shows a meagre value of p MO, i.e., 4%. The commercial photocatalyst of P25 as compared with cles reflects a degradation of 96%, which is nearly equal to the Cu/Zn Cu concentration. The visible light source was irradiated onto the Cu particles with MO dye in the solution, allowing the electrons to move valence band to a high energy conduction band. The charge carriers as render the property of reduction and oxidation in the conduction band respectively. The copper metal may improve the surface morphology cles, which could allow more light penetration to the active sites with gap. The p-type copper-doped ZnSe nanoparticles induce the proce reduction process for efficient catalytic activity. The rate of degrada using the pseudo-first order kinetics and the value of the rate consta lows: 0.01243 min −1 < 0.01300 min −1 < 0.1334 min −1 . Sample c has higher the other samples (Figure 10b), which shows better performance for p
The positively charged nanoparticles target the negatively charged bacteria, interacting by the electrostatic force of attraction. The interaction results in electron chain destruction, restricts DNA production, and damages the protein. The ROS formation may stop the multiplication/production of the bacteria, which leads to cell death [39].

Photocatalytic Dye Degradation
The photocatalytic dye degradation of Cu-doped ZnSe nanoparticles was examined against the MO dye under a visible light source using a xenon lamp above 400 nm. The degradation spectrum is shown in Figure 9. The MO dye absorbance decreased with the addition of a catalyst and increased time interval. The degradation activity of pristine ZnSe nanoparticles shows a decrease in absorbance by 75% for MO in 120 min [40]. The dye is slowly shown to lose its colour with increasing time. The presence of copper in Cu-doped ZnSe nanoparticles enhances the surface area and induces photo charge carriers to degrade MO dye, as depicted in Figure 10a,b. The % of photodegradation of the dye is estimated as 78% < 83% < 87% for different concentrations of Cu in ZnSe nanoparticles The photolysis process without the catalyst shows a meagre value of photodegradation of MO, i.e., 4%. The commercial photocatalyst of P25 as compared with Cu/ZnSe nanoparticles reflects a degradation of 96%, which is nearly equal to the Cu/ZnSe catalyst at 0.1 M Cu concentration. The visible light source was irradiated onto the Cu-doped ZnSe nanoparticles with MO dye in the solution, allowing the electrons to move from a low energy valence band to a high energy conduction band. The charge carriers as electrons and holes render the property of reduction and oxidation in the conduction band and valence band, respectively. The copper metal may improve the surface morphology of ZnSe nanoparticles, which could allow more light penetration to the active sites with a decrease in band gap. The p-type copper-doped ZnSe nanoparticles induce the process of oxidation and reduction process for efficient catalytic activity. The rate of degradation was calculated using the pseudo-first order kinetics and the value of the rate constant is enlisted as follows: 0.01243 min −1 < 0.01300 min −1 < 0.1334 min −1 . Sample c has higher kinetics values than the other samples (Figure 10b), which shows better performance for photodegradation.

Conclusions
The facile co-precipitation method was used to synthesize Cu-doped ZnSe nanopa ticles. The co-precipitation method has been found to be simple, less time-and energy consuming, sustainable, and economical compared with other conventional methods. Th copper integration was carried out on a ZnSe cubic structure. The structural modification

Conclusions
The facile co-precipitation method was used to synthesize Cu-doped ZnSe nanopar ticles. The co-precipitation method has been found to be simple, less time-and energy consuming, sustainable, and economical compared with other conventional methods. Th copper integration was carried out on a ZnSe cubic structure. The structural modification

Conclusions
The facile co-precipitation method was used to synthesize Cu-doped ZnSe nanoparticles. The co-precipitation method has been found to be simple, less time-and energyconsuming, sustainable, and economical compared with other conventional methods. The copper integration was carried out on a ZnSe cubic structure. The structural modifications were confirmed by XRD and the average crystallite size was estimated as 31 nm for 0.1 M Cu-doped ZnSe. The phase purity, optical transformations, and valency of the Cu-doped ZnSe nanoparticles revealed the structural modification of the catalyst. Different concentrations of Cu-doped ZnSe nanoparticles were used to study the catalytic activity. Among them, 0.1 M Cu-doped ZnSe nanoparticles have exhibited excellent photocatalytic activity towards MO dye. The 0.1 M Cu-doped ZnSe nanoparticles also exhibit noticeable antibacterial activity against the gram-positive and gram-negative bacteria. This work suggests that the Cu-doped ZnSe nanoparticles portray a prominent photocatalytic and antibacterial activity. Hence, the synthesized Cu-doped ZnSe nanoparticles can be used for developing a large-scale wastewater purification system for the degradation of contaminates.