Organic contaminants: photocatalytic degradation using HHP/CuONPs (2D/3D) composite as a heterogeneous catalyst

ABSTRACT Human hair is a filament rich in protein that grows from the follicles present in the scalp. It is considered to be a notable biomaterial consisting of β-keratin, which shows excellent catalytic activity in organic transformation. Keratin is a family of structural fibrous proteins rich in cysteine, which are abundantly present in human hair. Based on the template synthesis strategy, human-hair Keratin was used as a platform template to synthesise metal oxide nanoparticles. Here the aim was to synthesis hair protein supported CuO nanoparticles (HHP/CuONPs) and study their catalytic applications. Protein is extracted from the hair sample using the Shindai method. The HHP/CuONPs sample has been scrutinised using various characterisation techniques such as UV, FT-IR, SEM, TEM, EDX, Raman, XPS, and zeta potential. The synthesised HHP/CuONPs show photo-catalytic efficiency against coloured organic pollutants, 2,4-Dinitrophenol (DNP), and amaranth dye. The degradation level has been found to be 96% in DNP and 94% in amaranth dye. Optimisation and reusability of hair protein-mediated copper oxide have been tested under various conditions.


Introduction
Nanoparticles play a significant role in various fields of science, including analytic chemistry, medicine, and the agricultural & pharmaceutical sectors [1].This is due to the unique functional behaviour of nanoparticles/catalysis. Catalysis is a salient application of nanoparticles.Due to the higher surface area to volume ratio of these particles, they exhibit a driving force at an elevated temperature.However, sintering of nanoparticles may take place at lower temperatures over a shorter time scale.These particles also have the ability to exhibit size-related properties when compared to bulk particles [2,3].The larger surface area of nanoparticles helps increase responsiveness towards their catalytic activity [4].
Clay nanoparticles when induced into a polymer matrix increase reinforcement, leading to a higher grade of plastic that is verified using glass transition temperature [5].Nanoparticles obtained from these processes/procedures may be hard and do enhance the mechanical properties of the polymer.Some of the intrinsic attributes of nanomaterials pivot on the catalytic activity, such as bond length, atomic density, binding energy, thermal stability, diffusion, chemical reactions, photo absorption, Young's modulus, surface energy, surface stress, extensibility, compressibility of nano solid, etc. [6] There have been several methods of preparing nanoparticles, which include gas condensation, chemical precipitation, ion implantation, and pyrolysis [7].The products so obtained may be classified based on their physical and chemical properties.Conventional preparations of nanoparticles include the dispersion of preformed polymers and the polymerisation of the monomer.One such conventional method of preparation is human hair.
Human hair is an unpredictable tissue containing lipids, proteins, trace elements, and pigments [8].In tanneries, hair burning is a common practice, which results in residue containing a large number of COD, BOD, and TDS [9].Although it is highly accessible, and biodegradable, it is considered a waste biomaterial.However, improper transfer or accumulation may cause copious ecological issues, leading to contamination and lawful conflicts [10].In order to overcome these problems, human hair is used in cosmetics manufacturing, agriculture (fertiliser, pest control), and soil-water partitioning for the removal of organic pollutants and heavy metal pollutants from water.However, our study will focus more on the preparation and testing of these nanoparticles.
Copper is one of the few metals found in nature that can be used directly in its metallic form [11]. Though copper is primarily used in the manufacture of electrical wires, roofing, and plumbing for industrial machinery, metallic copper plays an important role in modern electric circuits due to its excellent electrical conductivity, Raman scattering, compatibility, and catalytic behaviour [12].Modern research gives a lot of attention to the above properties.When copper combines with oxygen, its chemical structure becomes more stable.The method used to make CuO nanoparticles has played a big part in the last 10 years because they can be used in both the medical and industrial fields [13][14][15][16].
An alternative strategy for controlled NP creation employs biologically based components.Peptides [17], proteins [18][19][20], and bacterial cells [21] have all been employed in the regulated synthesis of NPs.However, these methods are limited and rarely result in the formation of a homogeneous mixture.Proteins have a well-defined morphology as well as the ability to recognise other proteins.Furthermore, because of their specific reactivity towards target molecules, they are ideal contours for controlled NPs synthesis [18].Metal nanoparticles have been grown in the cavity of ferritin [22], a globular iron carrier 24-mer protein.Shoseyov and colleagues extracted the protein and showed that its cavity may be used as a template for the manufacture of a variety of metal-based nanoparticles [23].The pore size of SP1 is smaller than that of related protein-based carriers, such as ferritin, and it is more stable under harsh conditions.As a result, the SP1 permits smaller NPs to form, which are better for catalysis and other plasmonic effects.The SP1 protein's highly organised and stable structure, combined with its engineerable features, makes it an excellent platform to produce NPs, which can be used in a variety of research domains such as diagnostics, drug delivery, photonics, and catalysis.
This study aims to provide an modified synthesis of CuO nanoparticles.CuO nanoparticles exhibit excellent biological applications, such as antimicrobial actions against various ranges of pathogens and drug-resistant bacteria.However, the production of CuO nanoparticles is considered tedious due to surface oxidation.It has been tested that surface oxidation may be prevented by using stabilising agents as they have the ability to control the nucleation of particles.According to the literature, CuO NPs have strong photocatalytic activity, but the recombination rate is greater and the surface area is less.Keratin from human hair is one of the least soluble fibrous proteins in the majority of organic solvents.Furthermore, we anticipated that human hair would overcome the disadvantages of conventional supports such as alumina, polymers, carbon materials and silica.So, human hair protein was used to help solve these problems.The present study investigates the human hair protein (HHP) extract decorated CuO nanoparticles preparation [24][25][26], and it is reported to be a catalyst in the photocatalytic degradation of organic pollutants.

Chemicals and reagents
All reactions were performed at atmospheric conditions.Chemicals and solvents required were procured from SD Fine Chemicals, India.Shimadzu Ultraviolet (UV)-visible spectrometer used to measure UV-vis spectra.UV-irradiation has been performed using an 8-lamp photo reactor by Heber.The Hitachi F-7000 FL spectrometer was used to measure the luminescence property.The crystalline size of HHP/CuONPs was completed by XRD (Seifert Jso-Debyerex-2002).Supporting investigations of integrated nanoparticles were completed by Bruker Scanning Electron Microscopy (SEM), EDAX was identified using Oxford Instruments X-act 10 mm SDD.The surface morphology of HHP/CuO NPs was investigated by Transmission Electron Microscopy (TEM) FEI, Tecnai G2 mode.

Ball milling process
Human hair was collected from a local beauty parlour near our university campus in Vellore, India, and it was cut into small pieces.Later, it was ground in a ball mill for 46 h.The powdered hair washed with water, dried, and then used to get protein.

Extraction of protein
In the absence of sunlight, 10 g of human hair powder was cleaned well with distilled water and ethanol, and then it was dried at room temperature.To remove the dyes and lipids, the hair was washed with a mixture of methanol and chloroform.Dilapidated hair was mixed with 25 mM Tris-HCl (0.302 g in 50 ml of distilled water), 2.6 M Thiourea (1.97 g in 50 ml of distilled water), 5 M urea (3 g in 50 ml of distilled water), and 5% 2-Mercaptoethanol (2-ME, 5 ml in 45 ml of distilled water) and kept in an oil bath for 5 days at 50 • C. The mixture was filtered, centrifuged for 20 minutes, and dried at room temperature.This method for the production of protein from the hair was called the Shindai method [27] shown in Figure 1.The extracted hair proteins were utilised for the synthesis of protein-supported metal nanoparticles.

Synthesis of protein supported metal nanoparticles-HHP/CuONPs
After the extraction of protein, 500 mg of hair protein was collected in a 200 mL water containing 0.72 g of Cu(OAc) 2 .To enhance this reaction, the solution was kept in a microwave reactor at 300 W for a 5 min reaction time at 60°C.After 5 min, the solid nanocatalyst was filtered out and kept under calcination for 2 h at 250•C. Figure S1 depicts a schematic representation of the HHP/CuONPs synthesis.

Amaranth dye: photocatalytic performance
The amaranth dye was subjected to photocatalytic performance with the support of HHP/ CuONPs.The amaranth dye solution in aqueous medium of desired concentration (0.06 g/ L) has been developed using a stock solution.A pH range of 4 to 6 was prepared to vary the degradation of dye and, finally, to provide sufficient energy to excite HHP/CuO NPs.The prepared samples were irradiated under a UV lamp.Note down the initial time; with the regular interval, withdraw the dye solution (3 mL) and utilise it for UV analysis at 520 nm (λmax).The decrease in colour with respect to time was continuously monitored and it was concluded that the pH and concentration of the dye followed first-order kinetics.The experiment was performed in triplicates (average values reported) at room temperature.

Photocatalytic degradation of 2,4-Dinitrophenol
To attain the saturated solution, HHP/CuONPs were immersed in 2,4-Dinitrophenol (DNP).The photocatalytic performance of HHP/CuONP was demonstrated using DNP.The photochemical tests were carried out in a photoreactor with an annular shape and a multilamp (8 W, UV-C, manufactured by Heber, India).To optimise the parameters (pH, dose, time, and conc.), variations have been carried out in each parameter, as 5-8 (pH), 20-50 mg (photocatalyst dosages), 0-90 min (contact time), and 60-180 ppm (conc.DNP) were examined.NaOH and HNO 3 (1 M) were used to find the pH of synthetic solutions.Immediately after the photocatalytic reaction catalyst was separated using filtration, the reusable catalyst was washed with deionised water and ethanol several times, and dried in the air at 80 • C. The formation and mineralisation of the intermediate products formed at optimised parameters were further supported by the TOC analyser (Model Multi N/C, 3100 Germany).

Hydroxyl radical calculation and trapping studies
Trapping experiments were used to identify a radical that is responsible for hazard degradation and the generation of reactive species.In the trapping experiments, the consumption rate of hydroxyl radicals ( • OH), superoxide radicals (O 2 •− ), electrons (e − ), and holes (h + ) for colour and colourless organic molecules degradation was examined by the addition of 5 mmol/L of the respective, isopropyl alcohol (ISA for • OH quenching), ascorbic acid (ASC for O 2 •− quenching), K 2 Cr 2 O 7 for quenching of e − , and EDTA for h + quenching in a standard photocatalytic reaction solution [28,29].The efficiency of HHP/CuO NPs in hydroxyl radical production was determined using UVspectroscopic analysis [30].

Extraction of protein
The Shindai method is an effective process for protein development.It was technically synthesised through the reduced presence of denaturing agents and S-alkylation.Therefore, the amount of protein formed was observed to be non-uniform using these reagents, so the detergent had to be added during the extraction process.But it is found that the detergents interfere with the protein's chemical and physical studies, which has made the extraction process quite demanding.The benefit of the Shindai approach is that protein extraction takes place at the protein truancy.Protein extraction from hair is a simple procedure.The use of thiourea and urea in sufficient quantities has resulted in increased protein content in hair.The effect is not found in urea truancy.Both are important reagents for the amount of protein extracted.

Synthesis of HHP/CuONPs
Protein supported copper oxide nanoparticles were prepared by the redox method shown in Figure S2 [20].In general, the preparation mechanism of HHP/CuO NPs through subsequent oxidation of the sulphhydryl groups (−SH) in the reoriented hair is by exposure to air.Alternatively, a partial reduction in hair keratin disulphide bonds (-S-S-) took place without any additional reducing agent to obtain high efficiency nanoparticles [31].Human hair protein (HHP) is a good reducing agent in itself, which retains strong catalyst properties [32][33][34].

X-ray diffraction
An X-ray diffraction powder is used to check the sample crystallinity.Other major applications of these techniques include phase determination, compound purity, unit cell dimensional identification, and structural properties.A homogenised, grinded sample is used for analysis.The study was based entirely on Bragg's law: Another important equation to check the crystallinity of the molecule is the Scherrer equation by Paul Scherer.Scherrer's formula was used for calculating the size of the particles, and the size of the particles was calculated as 25-28 nm.The graph below depicts the XRD pattern of HHP/CuONPs in Figure 2. The four graphs show the XRD pattern for hair protein, protein supported CuO NPs, HHP/Cu 2 O and CuO NPs without any major support.The major peaks at 32•, 36• and 38• clearly show the formation of CuO NPs.The HHP/CuO NPs are slightly shifted due to the support of human hair proteins.The hkl values of the obtained peaks are 111, 110.The XRD was found to be consistent with the JCPDS No: 89-5899 [35].We confirmed the formation of HHP/Cu 2 O through XRD analysis, as per mechanism.The HHP /Cu 2 O were generated via the same synthesis process without calcination.3(c).It was clearly noted that the metal was effectively covered on the hair surface.For analysing the elements present, a small region of the hair sample has been isolated.We did obtain different elemental compositions and their weight percentages.Based on this weight percentage, the hair composition was calculated.Later, it is compared with the actual composition of the hair.It was also found that the actual hair composition and a calculated value based on the EDX (Figure 3(d)) were very similar.

Transmission electron microscopy
Figure 4 shows the TEM images of the hair-supported CuO nanoparticles.The figure clearly depicts the size range of the particles (the nanorange).The particle range was employed from TEM analysis, 25-30 nm.Particles of irregular size are also visible in some regions extracted from this experiment.The particles can be observed to be consistently arranged on the hair, which shows good attachment on the hair surface.Regulated loading of metal on the hair surface and NPs on the hair surface were effectively shielded.

Zeta potential and UV-DRS
The zeta potential is used to check the stability of the nanoparticles to know the physical properties of HHP, CuO and HHP/CuONPs. Figure S3 (a) depicts the zeta potential value at 14.9, 22.8, and 42.5 mV.This value clearly shows the maximum stability of the catalyst.It means that the stability of the catalyst is excellent in the reaction mixture to enhance the reaction rate at room temperature to give the product within one hour.After supporting the metal in the hair, the stability of the HHP/CuONPs shows good properties.As shown in Figure S3 (b), the bandgap values for HHP, CuO, and HHP/CuONPs as obtained from Tauc's plots are 2.51, 1.71, and 3.1 eV, respectively.The following Tauc's plot equation, where, h denotes that the Planck constant, ν denotes the photon's frequency, Eg denotes the band gap energy, and A denotes a constant.In the infrared region, the HHP-CuO composite shows tailing, this could be due to some charge transfer states between HHP and CuO due to their overlapping band alignment.

FT-IR
In the spectra of hair, the peaks at 3275 cm −1 indicate the presence of the -NH group.Figure S4 shows the C-H (-CH 2 ) group at 2922.16 cm −1 .The two peaks at 1625.99 cm −1 and 1536.34 cm −1 are the peaks of the -C = O and -CN groups, respectively.peaks of C-N, C-O, NH, O = C-N were noticed at 1230.58 cm −1 , C-S stretching bond showing at 511.14 cm −1 .In the spectra of CuO-coated hair, the peaks at 3477 cm −1 indicate the presence of the -OH group.The peak at 3564 cm −1 shows the peak of the -NH stretching group.The two peaks at 1597 cm −1 and 599 cm −1 were noticed for -CN and C-S stretching groups, respectively.

XPS analysis
The XPS analysis of HHP/CuO NPs is used to identify the chemical composition and oxidation state of the nanoparticles.Figure 5(a) depicts the XPS spectra of HHP/CuO NPs over the spectral regions of C1s, N1s, O1s, S 2p, Fe 2p, Si2p, Al 2p, and Cu 2p. Figure 5(g) shows that the Cu2P binding energies of the HHP/CuO nanocatalyst ranged between 920 and 980 eV.Especially the binding energy peaks at 951 and 931 eV correspond to Cu-2p 1/2 and Cu-2p 3/2 The spin-orbit doublets of Cu-2p 1/2 (962.44 and 951.64 eV), and 2p 3/2 (942.79 and 931.43 eV) confirm the presence of both Cu + and Cu 2+ ions in ceria lattice.The above-obtained results can be taken as evidence for the presence of both Cu + and Cu 2+ ions in the HHP (hair protein) lattice.Figure 5(d) depicts the XPS spectrum of S2p, with typical binding energies of S obtained at 169.02 eV due to the presence of sulphur in the hair protein.The binding energy at 0 to 180 eV corresponds to Si 2p, Al2p, and 2s.Due to the presence of Al in the hair protein, the specific peaks at 78. 26 & 38.99 eV and the XPS peak at 123.93 eV confirm the presence of Si ions.As shown in Figure 5(a,c,d, and b), the binding energy of C1s, O1s, S2p, and N1s peaks at 284.2, 531.44, 168.89, and 399.31 eV, respectively.From this XPS analysis, it was found that HHP/CuO NPs were formed.A co-ordination bond between the BE of the HHP and CuO nanoparticles was formed.

DTA/TGA analysis
The thermal stability of the HHP/CuONPs was analysed using a TGA (Thermo gravimetric analysis) at 0-800 • C (Fig. S5).The TGA profile indicates the weight loss percentage vs temperature, and the DTA indicates the temperature difference vs temperature.At first, a minimum amount of weight loss was detected at a temperature of 120 • C due to the evaporation of water molecules, which is approximately 3.397%.The peaks at 320 • C indicate the weight loss of the removal of volatile matter from HHP/CuONPs, which is approximately 32.22%.The highest weight loss of 64.40% at 670 • C indicates the phase transformation of the CuO with respect to the total loss of the sample.These results are evidence of the presence of hair protein in HHP/CuONPs.

BET (Brunauer-Emmett-Teller) analysis
The specific surface area of HHP/CuONPs was investigated by the N 2 adsorptiondesorption isotherm via BET surface area measurement as shown in Figure S6.From Figure S6, the specific surface area (SSA) of the HHP/CuO nanoparticles was calculated from the BET analysis, which was 13.645 m 2 /g.The total pore volume of the nanoparticles was found to be 7.717e-03 cc/g.The calculated pore size distribution is also provided at 8.440 Å and the average pore diameter is 12.242 Å.The comparative analysis is presented in Table S1.Spectra (e) Fe-2p Spectra (f) Si-2p Spectra (g) Cu-2p Spectra (h) survey spectra.

Raman analysis for HHP/CuONPs
The hair protein-mediated copper oxide nanoparticles were also verified by Raman analysis.The Raman spectra bands were observed to be sharp and intense in HHP/ CuO NPs. Figure S7 presents the Raman spectra of the HHP/CuONPs.In the Raman spectra, three major factors appeared.The essential highlights are identified by the proportion of D & G band intensities.Second, differences in the factual scattering intensities of different carbon patterns revealed interactions between nano metal oxides and hair protein carbon.
Finally, we focus on the location of CuO nanoparticles in Figure S7.The G band has been identified between 200 and 600 cm −1 .From this region, the strong peaks appeared at 287, 339, and 591 cm −1 that were responsible for the CuO of HHP/CuONPs.When compared to pure carbon, the D bands are slightly lower (1171, and 1157 cm −1 ).These results ascribe these shifts to the minor amount of carbon present in the CuO nanoparticles in comparison to HHP/CuONPs.These nanoparticles show a higher amount of the carbon shift, and in the lower region of the shifts, the also show CuO peaks clearly.These results show that the hair-protein carbon was the main component of the copper oxide nanoparticles that were made by hair proteins.

Photo catalytic application of HHP/CuONPs
In this study, the effect of HHP/CuONPs concentrations on the photocatalytic degradation of 2,4-dinitrophenol and amaranth on the irradiation of the visible light photo reactor, UV light photo-reactor, and natural sunlight was studied.The photocatalytic activity for the hair protein-mediated nanoparticles, the catalyst, ranges from 20-50 mg/L.Normally, the HHP/ CuO NPs are dispersed in DNP, and the amaranth solution is kept under the visible light reactor and photoreactor.Natural sunlight was sufficient for the photodegradation process.Here, the pH values and concentrations for DNP and dye solutions are modified.The UVvisible absorption maximum for the photo catalytic degradation of DNP and amaranth dye was 350 nm and 520 nm, respectively.Since the HHP/CuONPs showed good photocatalytic activity against both solutions.The HHP/CuONPs for the photocatalytic effect of the DNP and amaranth solution are shown in Figure (6 and 7).The reaction time for the photocatalytic activity process was found to be 90 mins in the DNP solution, with 96% degradation, dye solution with 94%, degradation efficiency of the photocatalyst.
Figure 6(a) depicts the change in the UV-Visible spectrum of amaranth dye (60 ppm) when exposed to UV light.Figure 6(b) depicts the C/C 0 relationship with respect to time.It was observed that 94% of the dye had been removed in the presence of light within 90 min, while adsorption had caused 1% of the dye to be removed without light.It can be confirmed that the increased efficiency of the amaranth dye is due to the presence of HHP/CuONPs under light irradiation.Around 96% was seen to be degraded under UV light within 90 min.Figure 7(a) indicates the changes in DNP (60 ppm) degradation with respect to time.In photocatalytic degradation, pH is one of the most important parameters for the effect of photocatalytic activity.The pH of the dye and DNP solution was tested at acidic, neutral, and basic levels.A concentration of 50 mg/L of the photocatalyst was used to reduce the concentration of DNP to 60 mg/L.At an acidic pH of 5, it showed maximum degradation of DNP (96%) which is shown in Figure 8.In addition, 50 mg/L of HHP/CuO nanocatalyst degraded 60 mg/L (0.06 /L) of amaranth dye in 90 min.Here, the pH of the amaranth dye also varied by three different naturalities.Maximum removal was obtained in the neural medium of the dye solution.To place the additional molecules on the surface of the catalyst, the concentration of the substrate has to be increased in a sufficient quantity [36].To achieve this, additional oxidiser species like • OH and O 2 •− are to be needed.In this case, at a specific catalyst load up and illumination power, the development of those radicals becomes stable and, as a result, develops a concentration that prompts a decrease in degradation.Some of the literature results showed similar results [37] explained that because of the absorption of ultraviolet radiation by the waste product rather than catalysts, the interval of the photocatalytic procedure was diminished.In some investigations, the lack of penetration of light and photocatalyst accumulation has been emphasised.Some literature upholds [38][39][40] our outcomes (Table 1).In addition, to find the adsorption efficiency of HHP/CuONPs, the model experiment has been carried out in the dark (absence of light).Also, it helped to find the ability of the pollutant to self-degradate, which was additionally inspected by a non-catalyst comparative test.In Figure 8, the degradation potency of HHP/CuONPs against dye and DNP was shown.The UV-Vis range of both DNP and amaranth displayed the declination in spectral concentrations with a time interval of photocatalytic degradation.The acquired outcomes disclose that HHP/CuONPs have better photocatalytic degradation capability than both HHP (Human Hair Protein) and CuO nanoparticles.CuO is doped with hair protein bases while the photocatalytic potential is regularly growing with the dopant attention of CuO.These outcomes give us an important conclusion that CuO has an extraordinary influence on the photocatalytic degradation of natural cancer agents and organic pollutants with hair protein.The development in photocatalytic ability is attributed to the reduction in bandgap strength of HHP/CuO NPs, which will increase the UV-light absorption potential in parallel [41,42].The acquired outcomes exhibit the presence of a synergistic effect between CuO and HHP heterojunction, which can efficiently upgrade the photocatalytic movement of HHP/CuONPs through encouraged charge bearer detachment between heterogeneous interfaces [43].In particular, 50 mg of CuO doped in HHP indicates a higher degradation efficiency of about 94% for amaranth and 96% for DNP, which is greater than different as-synthesised nanostructures.

Mineralisation of 2,4-DNP and amaranth
DNP and amaranth dye mineralisation were made possible by advanced oxidation processes (AOPs) [44].The mineralisation rate in both processes depends on the technique of degradation, the source of radiation, and the pollutants' concentration.In this investigation, mineralisation of 2,4-DNP and amaranth dye under selected conditions was measured and attained to 92.82 and 92.03% TOC removal, during 90 min.Therefore, it may be all over that the required mineralisation through HHP/CuONPs was obtained.In alternative studies, percentages of TOC removal were achieved 20, 50, and 76%, severally [45,46].

Postulated reaction mechanism
Based on the above investigation (Figure S8) the following mechanism for hair proteinmediated photo-catalytic degradation is suggested: Upon visible light irradiation, HHP/ CuONPs can be excited to form a state of transition, which will decrease Cu 2+ by the  metallic and charge transfer process.Due to the weak forces developed between copper and organic materials, there will be a release of free copper ions into the solution, which triggers the corresponding photocatalytic response.The • OH radicals produced during the photocatalytic process attack DNP and amaranth pollutants, which lead to product degradation.It was observed that during the initiation phase, the generation of Cu 2+ was found to be minimal enough to cause fast degradation of amaranth and DNP.The attached • OH radicals caused the oxidative degradation of DNP, which was considered a highly reactive electrophilic oxidant in the Fenton process.The three substituents present in DNP activate the ring through the attack of the electrophilic ) are known to be prominent reactive species that are involved during the degradation of organic molecules.
In addition, major influences on photocatalytic behaviour include redox reactions on the photocatalyst surface, where organic compounds are eventually decomposed by certain reactive species such as h +, • OH, and (O 2 •− ), photocatalytic oxidation [19].
Trapping experiments were performed to determine the most reactive species of HHP/CuONPs for amaranth, DNP, and triazole degradation to elucidate the mechanisms of the photocatalyst.With the introduction of different quenchers under visible light irradiation and the findings of trapping studies, photocatalytic degradation of amaranth, DNP, and triazole degradation by HHP/CuONPs has been achieved (Figure S10).Trapping studies revealed that photo-generated holes (h + ), electrons (e), superoxide radicals (O 2 •− ) or hydroxyl radicals ( • OH) were primary active species for amaranth, DNP, and triazole photodegradation by the HHP/CuONPs catalyst.Fig. S11.
shows that noticeably hindered photoactivity, indicating the main role of • OH and h + in the photodegradation cycle.ASC inhibited photoactivity to a lesser extent, suggesting that the reactive species (O 2 •− ) are not primarily involved in the degradation process.In contrast, no photo-reduction hindrance was identified in the presence of K 2 Cr 2 O 7 , indicating the minimal role played by e − in the photodegradation cycle.Based on the above experimental results, the HHP/CuONPs photocatalyst suggested a possible mechanism to enhance the photocatalytic degradation of amaranth, DNP, and triazole.HHP/CuONPs could be stimulated by UV-light (365 nm) to produce photogenerated electrons and holes (Eq 1).CuO NPs will act as electron traps, capable of trapping excited electrons (Eq 2) and enabling the separation of electron-hole pairs, thus facilitating the transfer of charges from the HHP into the photocatalyst's surface.The photo-induced electrons transferred from the CuO to the photocatalyst surface could thus trap and decrease the adsorbed O 2 to O 2 •− (Eq 3), while the generated (O 2 •− ) would participate in degradation reactions (Eq 5).At the same time, photogenerated holes after transport to the photocatalyst surface could also react with H 2 O to form • OH (Eq 4) for degradation of amaranth, DNP, and triazole (Eq 7) or directly oxidise dyes and compounds (Eq 5).According to trapping experiments, holes and superoxide radicals were thought to be the predominant reactive species for amaranth, DNP, and triazole degradation (Eq 5 & 6), whereas hydroxyl radicals could also play minor roles in the degradation cycle (Eq 7).Finally, chemical compounds could be mineralised into CO 2 , H 2 O, or mineral acids.The proposed photocatalytic mechanism for degradation of HHP/CuONPs could be defined as follows.

Recyclability of the catalyst
With respect to the previously mentioned statements, we investigated the recycling of HHP/CuONPs for the degradation of organic dyes (Figure 9).The catalyst was removed from the product, after the completion of the reaction.The rest of the catalyst was washed with ethyl acetate and exposed to the next run.The recovered catalyst was reused up to five times without any considerable loss of its catalytic activity (Figure 9).Furthermore, the recycled catalyst has been examined by X-ray diffraction.As shown in Fig. S12, the XRD range of reused HHP at CuO displays excellent concurrence with the XRD spectrum of fresh HHP/CuO NPs (Figure S2).The stability of HHP/CuO after reutilising was verified by the position of hkl values in XRD for the fresh and recycled catalyst.This current study is powerful proof of the high stability of HHP/CuONPs after being reused.

GC-MS analysis of degradation products
Before the degradation experiment was carried out, GC-MS was performed.The dye was declared as amaranth and 2,4 dinitrophenol.Figure S13 (a-f) shows the mass spectrum of the dye diluted in methanol, scanned from m/z 50 to m/z 1200 in positive ion mode.The molar mass of amaranth and 2,4 dinitrophenol dye were 604.4730 g mol −1 and 184.107 g mol −1 .It is not unusual to observe in positive electrospray mass spectrometry the molecules with sodium replaced by protons with one more proton or sodium to cationize them.The mass spectrometer used was equipped with unit resolution quadrupole analysers.Hence, the expected species could be of m/z 597 [M + H] + and m/z 186 [M + H] + .Figure S13 (c&f) suggests a degradation product of Amaranth and 2,4 dinitrophenol do not match the before degradation molar mass product.

Conclusions
Human hair protein nanoparticles supported by copper oxide have been successfully prepared.The HHP/CuO system is found to be an efficient heterogeneous photocatalyst and a good absorbent for various colour degradations.Amaranth and DNP degradation as a photocatalyst has experimented with UV/visible light /natural sunlight irradiation.Due to its superior photocatalytic activity, the catalyst was found to be efficient for removing high dye concentrations.The catalyst plays an important part in the reaction.Catalyst optimisation was also conducted under various conditions.The photocatalytic mechanism of HHP/ CuONPs is proposed based on UV-Vis, DRS, PL, reactive species trapping experiments, and • OH radical production analysis.This research work provides a new path for the design and production of photocatalysts with supreme charge carrier separation and migration ability.

Figure 3 Figure 2 .
Figure3represents the SEM image of HHP@CuO NPs.In this image, the metal loading capacity on the hair surface and the catalyst's chemical composition are clearly explained.The main elements present in the hair are C, N, O, and S. Actual chemical compositions (approx.) of these elements are C-45%, S-7%, N-15%, O- 28%. Figure 3(a) shows the SEM image of hair without any metal content.EDX analysis reveals the elements present in hair.C, N, O, and S are the major elements.From EDX Figure 3(b), the weight percentage of the elements was noted.The SEM image of the Cu-supported hair is shown in Figure

Figure 7 (
b) depicts the C/C 0 variation over time in the presence of HHP/ CuONPs.It supports HHP/CuONPs by acting as a good photocatalyst.Figures6(c) and 7(c) show the variation between C/C0 and time for various parameters of amaranth dye and DNP.Amaranth & DNP undergo remarkable degradation in the presence of HHP/CuONPs under light-medium.Within 90 min, around 53% (visible medium) and 35% (natural sunlight) of amaranth dye were successfully degraded, whereas DNP was degraded at 62 & 38%.The HHP/CuONPs with different amounts of weight were analysed for the treatment of photocatalytic activity.The catalytic activity of HHP/CuO NPs is better in 50-60%.All measurements were performed with 50 wt % HHP/CuO NPs.

Figure 6 .
Figure 6.(a) UV-visible absorption spectra of amaranth (b) Plot of C/C 0 vs. time (c) Isotherm fitting model.All the experiment was done with 60 ppm dyes with 50 mg of HHP/CuONPs.

Figure 7 .
Figure 7. (a) UV-visible absorption spectra of DNP (b) Plot of C/C 0 vs. time (c) Isotherm fitting model.All the experiment was done with 60 ppm dyes with 50 mg of HHP/CuONPs.

Table 1 .
Comparison study for Photo catalytic degradation.
• OH radical.A photoluminescence (PL) analysis was carried out to study the photocatalysts photo-induced charge carrier separation efficiency.FigureS9depicts the PL spectra of the synthesised photocatalyst HHP/ CuONPs and CuO.HHP/CuONP's showed a high-intensity broad photoluminescence peak at 294 nm.Hair protein had an intrinsic geometrical structure due to which the nanoparticle exhibited high intensity.The photoinduced charge carrier recombination was suppressed, causing the PL intensity to decrease.Generally, hydroxyl radicals ( • OH), holes (h + ),