Activated Carbon-Loaded Titanium Dioxide Nanoparticles and Their Photocatalytic and Antibacterial Investigations

Activated carbon doping TiO2 nanoparticles were synthesised by zapota leaf extract using the co-precipitation method. The bio-constituents of plant compounds were used in the reactions of stabilization and reductions. The carbon loading on the TiO2 nanoparticles was characterised by XRD, FTIR, UV-DRS, SEM with EDX, and TEM analysis. The loading of activated carbon onto the TiO2 nanoparticles decreased the crystallite size and optical bandgap, and their doping improved the surface structure of AC/TiO2 nanoparticles. Mesoporous/microporous instability was remodified from the activated carbon, which was visualised using SEM and TEM analysis, respectively. The photocatalytic dye degradation of Rh-B dye was degraded in TiO2 and AC/TiO2 nanoparticles under visible light irradiation. The degradation efficiencies of TiO2 and AC/TiO2 nanoparticles were 73% and 91%, respectively. The bacterial abilities of TiO2 and AC/TiO2 nanoparticles were examined by E. coli and S. aureus. The water reclamation efficiency and bactericidal effect of TiO2 and AC/TiO2 nanoparticles were examined via catalytic dye degradation and bacterial efficiency of activated carbon-doped titanium dioxide nanoparticles.


Introduction
Water scarcity is an important and big issue in the current world. The demand for water is influenced by the development of industries and population increments [1][2][3][4][5][6]. Technology and population growth affect water bodies through various associated compounds. Dyes, germs, chemicals, and parasites are among the components that are integrated into water bodies and changed to unpleasant and non-drinkable water. Dyes, chemicals, microbes, and parasites are among the components that are integrated into water bodies and changed into unpleasant and non-drinkable water [7][8][9][10]. Among the pollutants, organic and biological compounds are very toxic to living organisms. Inadequacies in the water system have been remedied through the application of nanomaterials for either wastewater treatment or water reuse systems. Numerous technologies are elaborate in the water reclamation process, such as filtrations, coagulations, adsorption, and photocatalysts [11,12]. The photocatalyst method is an efficient technique and more powerful and convenient than other remediation processes. In addition, the photocatalyst remediation process derives non-toxic compounds,

Materials
All the chemicals were procured from Merck India. The reductant of Manilkara zapota leaf was collected from Tamilnadu, India. Synthesised chemicals of activated carbon and titanium tetra isopropoxide (TTIP) were used at an analytical grade (AR). Double distilled water was used for further synthesis, and extra modifications did not occur in the synthesised process.

Manilkara Zapota Leaf Extract Preparation
A total of 500 mg of fresh Manilkara zapota leaf was collected from a garden. The obtained leaves were washed with tap water, rinsed with double distilled water, and then dried at room temperature for 6 h. Finally, dried samples were mixed with 200 mL of double distilled water and heated to 100 • C for 60 min. The boiled extract was filtered by Whatman No.1 filter paper and stored for further synthesis processes.

Synthesis of TiO 2 Nanoparticles
The 1 M TTIP solution was dissolved in 90 mL of double distilled water and mixed with 10 mL of plant extract. The mixed solution was stirred for 6 h, and the temperature was maintained at 60 • C. Ti compounds slowly reduced their colour configuration to a milkwhite colour formation. After stirring the colour-reduced solution, it was centrifuged for 10,000 rpm for 180 s, and this was repeated three times to eliminate unwanted compounds from the surface. Then, the precipitate was processed using double distilled water and dried at 80 • C for one day. Finally, the obtained nanophase powder was stored for further characterizations.

Preparation of AC/TiO 2 Nanoparticles
An amount of 2 g of the activated carbon source was poured into a 1 M TTIP solution and 10 mL of plant extract. The combined source solution was stirred for 6 h at 60 • C, which produced the precipitate form of AC/TiO 2 nanoparticles. The nano precipitate was purified from the centrifugation process for 10,000 rpm at 180 s (3 times) and washed with double distilled water. The purified precipitate obtained after removing the supernatant was kept in an oven at 800 • C for 24 h. The final AC/TiO 2 nanoparticles were stored for further measurements.

Characterization of AC/TiO 2 Nanoparticles
The phase details and structural information were monitored from X-ray diffraction (XRD-PANalytical B.V., Overijssel, The Netherlands). The chemical compounds and their functionality compounds and groups were captured from Fourier transform infrared (FT-IR-Perkin Elmer, Waltham, MA, USA). The optical imperfections and their electronic mitigations were recorded using UV-DRS (UV-2700, Shimadzu, Kyoto, Japan) analysis. The surface morphology and their modifications of the synthesised nanoparticles were derived from transmission electron microscopy (TEM-FEI Titan 80-300, Bangalore, India), and scanning electron microscopy (SEM-Carl Zeiss, Jena, Germany) coupled with EDAX spectroscopy measured the elemental presence of the nanoparticles. Binding energy and their bonding were measured from XPS (Physical Electronics Model-PHI 5000 Versa Probe III-Chanhassen, MN, USA)

Bacterial Suspension
The antibacterial activity was determined using Escherichia coli 745 and Staphylococcus aureus 9779 as bacterial sources. Layreint Broth (LB) medium was used to prepare the Gram-positive S. aureus and Gram-negative bacteria E. coli under the conditions of 36 • C/48 h. The well diffusion method helped to determine the bacterial efficacy of synthesised nanoparticles. The well wall was created using a cork borer, and its diameter was 0.85 cm on the Petri plates. The different concentrations (10,25,50, and 100 µL) of the nanoparticles sample were loaded into the created well and incubated for 24 h at 36 • C. The bacterial growth rate was calculated using the zone of inhibitions, and the range was measured in millimetres.

Photocatalytic Degradation Experiment
The visible light photocatalytic dye degradation of Rh-B dye was treated under solar irradiation. The 10 mL (dye concentration was 1 × 10 −5 M) Rh-B solution was dissolved in 10 mg of nanoparticles and placed in a dark condition to reach the equilibrium positions. After that, the mixed solution was irradiated by solar light with continuous stirring. At 5 min, the aliquot was taken out and centrifuged to remove the nanoparticles, and the degradation efficiency was measured by the following formula. The quenching experiment helps to find the active species (superoxides, free radicals, and holes) of the photocatalyst. The 1 mmol/L concentration quenchers (triethanolamine (TEOA), p-benzoquinone (BQ), and (isopropyl alcohol (IPA)) were used in the analysis, and their measurements were captured from UV-Visible spectroscopy.  Figure 1 shows the X-ray diffraction pattern of titanium dioxide and activated carbondecorated titanium dioxide nanoparticles. The pure titanium dioxide nanoparticles obtained diffractive patterns at 2θ = 25.  [31,32]. The anatase phase stability is very high compared to other phases of titanium dioxide nanoparticles, which can accelerate the electron accumulations on the surfaces. The doping of activated carbon reformed the titanium dioxide nanoparticles lattice arrangement, which can be coated on the titanium dioxide surfaces. The activated carbon existence was confirmed by 2θ = 25.33 T (0 0 2), which moved towards the lower wavelength side. The peak displacement on the titanium dioxide surfaces provides evidence of the formation of activated carbon doping on the surfaces. The obtained 2θ values ensured the activated carbon presence and were confirmed by the standard JCPDS card number 75-1621 [33][34][35]. The activated carbon increased the electron accumulations on the surface and modified the crystal regularity. The crystallite sizes of the nanoparticles were calculated using the Scherrer formula. The calculated crystallite sizes are 29 nm and 23 nm for TiO 2 and AC/TiO 2 nanoparticles, respectively. The incorporation of activated carbon increased the lattice orderings and decreased the void between atoms, which deducted the crystallite sizes. The enhanced crystallite sizes of the AC/TiO 2 nanoparticles are an efficient alternative for water remediation and biological inactivation activities.

XRD Analysis
The quenching experiment helps to find the active species (superoxides, free radicals and holes) of the photocatalyst. The 1 mmol/L concentration quenchers (triethanolamin (TEOA), p-benzoquinone (BQ), and (isopropyl alcohol (IPA)) were used in the analysis and their measurements were captured from UV-Visible spectroscopy. Figure 1 shows the X-ray diffraction pattern of titanium dioxide and activated car bon-decorated titanium dioxide nanoparticles. The pure titanium dioxide nanoparticle obtained diffractive patterns at 2θ = 25.44ᶿ, 38ᶿ, 47.94ᶿ, 54.13ᶿ, 54.81ᶿ, 62.75ᶿ, 69.08ᶿ, 70.8ᶿ and 74.84ᶿ values, which are associated with (1 0 1), (0 0 4), (2 0 0), (1 0 5), (2 1 1), (2 0 4 (1 1 6), (2 2 0), and (2 1 5) planes, respectively. The obtained values coincided well wit the anatase phase standard JCPDS card number: 89-4921 and their tetragonal structur [31,32]. The anatase phase stability is very high compared to other phases of titanium di oxide nanoparticles, which can accelerate the electron accumulations on the surfaces. Th doping of activated carbon reformed the titanium dioxide nanoparticles lattice arrange ment, which can be coated on the titanium dioxide surfaces. The activated carbon exist ence was confirmed by 2θ = 25.33ᶿ (0 0 2), which moved towards the lower wavelengt side. The peak displacement on the titanium dioxide surfaces provides evidence of th formation of activated carbon doping on the surfaces. The obtained 2θ values ensured th activated carbon presence and were confirmed by the standard JCPDS card number 75 1621 [33][34][35]. The activated carbon increased the electron accumulations on the surfac and modified the crystal regularity. The crystallite sizes of the nanoparticles were calcu lated using the Scherrer formula. The calculated crystallite sizes are 29 nm and 23 nm fo TiO2 and AC/TiO2 nanoparticles, respectively. The incorporation of activated carbon in creased the lattice orderings and decreased the void between atoms, which deducted th crystallite sizes. The enhanced crystallite sizes of the AC/TiO2 nanoparticles are an efficien alternative for water remediation and biological inactivation activities.   Figure 2 displays the functional groups of the TiO 2 and AC/TiO 2 nanoparticles. The broad peak of pure TiO 2 nanoparticles located at 3238 cm −1 exhibited OH-stretching on the nanoparticles' surface, which absorbed the phenolic compounds, alcohols, and water molecules [36,37]. An aromatic ring vibration at the C=C stretching peak was seen at 1634 cm −1 , carboxylic acid formation was seen at 1524 cm −1 , and C-H asymmetric stretching from the plant derivatives was exhibited at the peak of 1417 cm −1 , which was derived from the zapota plant extract [38][39][40]. The wide peak at 759 cm −1 and the narrow peak at 553 cm −1 indicated the formation of activated carbon-loaded titanium dioxide nanoparticles and established the oxygen-metal-oxygen bonding [41]. The activated carbon loading modified the adsorption capability of TiO 2 nanoparticles. The peak of 2984 cm −1 decreased their intensity due to the doping of activated carbon and derived the OH-stretching on the surface [42]. The 1731 cm −1 peak indicates the existence of amine compounds from biomolecules. The 1365 cm −1 peak represents the secondary amide compounds derived from phenolic plant compounds. The peak at 1218 cm −1 denotes the stretching vibrations of the C-O bond [43][44][45]. The peaks at 898 cm −1 and 516 cm −1 characterised the C-O-Ti-O bonding [46], which recognised the formation of activated carbon-loaded titanium dioxide nanoparticles. Activated carbon loading or substitution on titanium oxide nanoparticles was obtained from plant bio-molecules. Figure 2 displays the functional groups of the TiO2 and AC/TiO2 nanoparticles. The broad peak of pure TiO2 nanoparticles located at 3238 cm −1 exhibited OH-stretching on the nanoparticles' surface, which absorbed the phenolic compounds, alcohols, and water molecules [36,37]. An aromatic ring vibration at the C=C stretching peak was seen at 1634 cm −1 , carboxylic acid formation was seen at 1524 cm −1 , and C-H asymmetric stretching from the plant derivatives was exhibited at the peak of 1417 cm −1 , which was derived from the zapota plant extract [38][39][40]. The wide peak at 759 cm −1 and the narrow peak at 553 cm −1 indicated the formation of activated carbon-loaded titanium dioxide nanoparticles and established the oxygen-metal-oxygen bonding [41]. The activated carbon loading modified the adsorption capability of TiO2 nanoparticles. The peak of 2984 cm −1 decreased their intensity due to the doping of activated carbon and derived the OH-stretching on the surface [42]. The 1731 cm −1 peak indicates the existence of amine compounds from biomolecules. The 1365 cm −1 peak represents the secondary amide compounds derived from phenolic plant compounds. The peak at 1218 cm −1 denotes the stretching vibrations of the C-O bond [43][44][45]. The peaks at 898 cm −1 and 516 cm −1 characterised the C-O-Ti-O bonding [46], which recognised the formation of activated carbon-loaded titanium dioxide nanoparticles. Activated carbon loading or substitution on titanium oxide nanoparticles was obtained from plant bio-molecules.

UV-DRS Analysis
The UV-DRS measurements of synthesised TiO2 and AC/TiO2 nanoparticles are displayed in Figure 3. Figure 3a exposes the optical insights of the synthesised nanoparticles,

UV-DRS Analysis
The UV-DRS measurements of synthesised TiO 2 and AC/TiO 2 nanoparticles are displayed in Figure 3. Figure 3a exposes the optical insights of the synthesised nanoparticles, and their optical limit was characterised by the ultraviolet and visible regions. The pure TiO 2 nanoparticles exhibited an absorption edge at 370-390 nm, which described the green emission of TiO 2 nanoparticles. In addition, the O-Ti-O formations of Ti 4+ cations established the UV region absorption in TiO 2 nanoparticles. Activated carbon doping to the Ti 4+ cations increased the electron excitations and produced a higher quantity of charge carriers than pure TiO 2 nanoparticles. When activated carbon is added to the Ti 4+ cationic system, the peaks shift to the higher wavelength side (redshift). Furthermore, the Ti 4+ cations increased the adsorbing behaviour due to their modifications of crystal lattices by doping activated carbon. The optical defect and electron migrations are well constructed by calculating the bandgap of the nanoparticles. The Kubelka-Munk relations were used to find the bandgap of synthesised nanoparticles. The obtained values are demonstrated in Figure 3b. The pure anatase TiO 2 is 3.11 eV, well matched with the previous TiO 2 nanoparticle value and standard anatase bandgap of TiO 2 nanoparticles [47][48][49][50][51]. The wide bandgap of TiO 2 nanoparticles was modified with the activated carbon, which reduced the bandgap to 2.73 eV. The energy difference is 0.38 eV which established the visible light absorption and evidenced the production of photo-charge carriers. The generations of charge carriers increased the free radicals and enhanced the recombination activity, which provoked efficient catalytic degradation activity [52]. The radical generation promotes bactericidal activity and is highly appreciable in biomedical developments. emission of TiO2 nanoparticles. In addition, the O-Ti-O formations of Ti 4+ cations established the UV region absorption in TiO2 nanoparticles. Activated carbon doping to the Ti 4+ cations increased the electron excitations and produced a higher quantity of charge carriers than pure TiO2 nanoparticles. When activated carbon is added to the Ti 4+ cationic system, the peaks shift to the higher wavelength side (redshift). Furthermore, the Ti 4+ cations increased the adsorbing behaviour due to their modifications of crystal lattices by doping activated carbon. The optical defect and electron migrations are well constructed by calculating the bandgap of the nanoparticles. The Kubelka-Munk relations were used to find the bandgap of synthesised nanoparticles. The obtained values are demonstrated in Figure 3b. The pure anatase TiO2 is 3.11 eV, well matched with the previous TiO2 nanoparticle value and standard anatase bandgap of TiO2 nanoparticles [47][48][49][50][51]. The wide bandgap of TiO2 nanoparticles was modified with the activated carbon, which reduced the bandgap to 2.73 eV. The energy difference is 0.38 eV which established the visible light absorption and evidenced the production of photo-charge carriers. The generations of charge carriers increased the free radicals and enhanced the recombination activity, which provoked efficient catalytic degradation activity [52]. The radical generation promotes bactericidal activity and is highly appreciable in biomedical developments.

SEM with EDX and TEM Analysis
The synthesised nanoparticles' surface morphology and their elemental disorder properties were measured from SEM with EDX spectrum, as shown in Figure 4. The pure TiO2 nanoparticles exhibited semi-spherical and spherical shapes on the surface. The semispherical shapes were attained from the plant molecules. The plant molecules' infringement over the surface creates a large molecule, and their existence builds semi-spherical

SEM with EDX and TEM Analysis
The synthesised nanoparticles' surface morphology and their elemental disorder properties were measured from SEM with EDX spectrum, as shown in Figure 4. The pure TiO 2 nanoparticles exhibited semi-spherical and spherical shapes on the surface. The semispherical shapes were attained from the plant molecules. The plant molecules' infringement over the surface creates a large molecule, and their existence builds semi-spherical formations of TiO 2 nanoparticles [53,54]. The distribution and spherical formations are displayed in Figure 4a,b. The addition of activated carbon to the TiO 2 nanoparticles formed an equal spherical shape and even distribution over the nanoparticles' surface, as shown in Figure 4c,d. The pure TiO 2 nanoparticles demonstrated that the particle size is 30 nm and AC/TiO 2 is 22 nm, which are close to the XRD crystallite size values. The energy dispersion on the elements was characterised by EDX spectroscopy, and their spectrum and table are presented in Figure 4e. The carbon, titanium, and oxygen elements were confirmed from the EDX peaks and table. The low amount of carbon modified the surface morphology and created a mono-dispersion over the surfaces. formed an equal spherical shape and even distribution over the nanoparticles' surface, as shown in Figure 4c,d. The pure TiO2 nanoparticles demonstrated that the particle size is 30 nm and AC/TiO2 is 22 nm, which are close to the XRD crystallite size values. The energy dispersion on the elements was characterised by EDX spectroscopy, and their spectrum and table are presented in Figure 4e. The carbon, titanium, and oxygen elements were confirmed from the EDX peaks and table. The low amount of carbon modified the surface morphology and created a mono-dispersion over the surfaces. The TEM images of AC/TiO2 nanoparticles are displayed in Figure 5a,b. Figure 5a revealed that AC/TiO2 nanoparticles are spherical in shape with dark spotted surfaces. Dark spotted surfaces indicated activated carbon doping on the TiO2 nanoparticles. The TEM particle size of AC/TiO2 nanoparticles is 22 nm. The hetero-compounds of activated carbon-doped titanium dioxide nanoparticles formed the improved morphology. The polycrystalline and obtained AC/TiO2 nanoparticles' structural information was ensured by the SAED pattern of AC/TiO2 nanoparticles, as shown in Figure 5b. The obtained particle sizes are well matched with the XRD crystallite size and SEM particle size. The spherical nanoparticles have large surface areas. The surface enhancement of nanoparticles simply strikes the organic pollutants or bacterial system and induces the charge carrier's productivity [55][56][57]. The spherical nanoparticles demonstrated an improved catalytic activity compared to other shaped nanoparticles. The TEM images of AC/TiO 2 nanoparticles are displayed in Figure 5a,b. Figure 5a revealed that AC/TiO 2 nanoparticles are spherical in shape with dark spotted surfaces. Dark spotted surfaces indicated activated carbon doping on the TiO 2 nanoparticles. The TEM particle size of AC/TiO 2 nanoparticles is 22 nm. The hetero-compounds of activated carbon-doped titanium dioxide nanoparticles formed the improved morphology. The polycrystalline and obtained AC/TiO 2 nanoparticles' structural information was ensured by the SAED pattern of AC/TiO 2 nanoparticles, as shown in Figure 5b. The obtained particle sizes are well matched with the XRD crystallite size and SEM particle size. The spherical nanoparticles have large surface areas. The surface enhancement of nanoparticles simply strikes the organic pollutants or bacterial system and induces the charge carrier's productivity [55][56][57]. The spherical nanoparticles demonstrated an improved catalytic activity compared to other shaped nanoparticles.

XPS Analysis
The chemical composition and the valency of the synthesised AC/TiO 2 nanoparticles were determined from X-ray photoelectron spectroscopy. The XPS spectrum consists of wide Ti-2p, O-1s, and C-1s spectra for AC/TiO 2 nanoparticles, representing activated carbon, titanium, and oxygen, as shown in Figure 6. The Ti-2p spectrum is associated with oxygen and activated carbon, increasing the bonding between the synthesised nanoparticles. The Ti-2p spectrum is located at 458.6 eV (Ti-2p 3/2) and 466 eV (Ti-2p 1/2). The lattice oxygen spectrum is exhibited at 531 and 533 eV for O-1s, and their association in C=O and O-C=O is derived from activated carbon and plant extract. Their inclusion over the lattice oxygen stabilised the Ti 4+ valency and improved the degradation of the organic dyestuffs. The activated carbon spectrum is located at 235 eV and represents the C-1s elements, which indicates the formation of activated carbon-doped TiO 2 nanoparticles. When doping the TiO 2 nanoparticles, activated carbon emanates the strongest binding between them. The

XPS Analysis
The chemical composition and the valency of the synthesised AC/TiO2 nanoparticles were determined from X-ray photoelectron spectroscopy. The XPS spectrum consists of wide Ti-2p, O-1s, and C-1s spectra for AC/TiO2 nanoparticles, representing activated carbon, titanium, and oxygen, as shown in Figure 6. The Ti-2p spectrum is associated with oxygen and activated carbon, increasing the bonding between the synthesised nanoparticles. The Ti-2p spectrum is located at 458.6 eV (Ti-2p 3/2) and 466 eV (Ti-2p 1/2). The lattice oxygen spectrum is exhibited at 531 and 533 eV for O-1s, and their association in C=O and O-C=O is derived from activated carbon and plant extract. Their inclusion over the lattice oxygen stabilised the Ti 4+ valency and improved the degradation of the organic dyestuffs. The activated carbon spectrum is located at 235 eV and represents the C-1s elements, which indicates the formation of activated carbon-doped TiO2 nanoparticles. When doping the TiO2 nanoparticles, activated carbon emanates the strongest binding between them. The constructed results of Ti-2p, O-1s, and C-1s demonstrate the potential of their binding energy and the degradation potential of the AC/TiO2 nanoparticles.

Antibacterial Activity
The synthesised pure AC, plant extract, TiO2, and AC/TiO2 nanoparticles were examined against S. aureus (G-Positive) and E. coli (G-Negative) bacterial strains. The obtained

Antibacterial Activity
The synthesised pure AC, plant extract, TiO 2 , and AC/TiO 2 nanoparticles were examined against S. aureus (G-Positive) and E. coli (G-Negative) bacterial strains. The obtained bacterial results of the synthesised nanoparticles are displayed in Figures 7 and 8. The AC and plant extract (zapota) bacterial activities act as a standard antibacterial module, and it was compared with pure TiO 2 and AC/TiO 2 nanoparticles. The zone of inhibitions was evident by the inactivation of bacterial strains. Anatase TiO 2 nanoparticles revealed the highest activity in E. coli (G-Negative) bacterial strains compared to S. aureus (G-Positive) bacterial strains. The wide bandgap and extended recombination process formulated radical activity, which enhanced biological deactivation [58][59][60] as the activated carbon-doped titanium dioxide nanoparticles exhibited higher activity in E. coli than in S. aureus. The presented zone of inhibitions is based on the dosage-dependent manner, and their dissolution rate decides the bacterial dissociations. The antibacterial activity is AC < plant extract < TiO 2 < AC/TiO 2 nanoparticles. Every action is based on some procedure and protocol of the event. The bacterial inactivation mechanism is displayed in Figure 9. The entry of nanoparticles attacks the cell wall, and their strength disrupts the cell wall bonding. The leakage of the cell wall permits the entry of nanoparticles into the bacterial domain, which affects electron chain communications. The miscommunications in the cell system stop DNA and protein production, which affects the cell-nutrient system. A nutrient-free cell system gradually expresses its inactivation. Regarding the obtained findings, activated carbon-doped titanium dioxide nanoparticles improved their bio-sorption nature, and it is highly advisable to use bio-medical development-related devices [60][61][62].

Photocatalytic Activity
The pure AC, TiO2, and AC/TiO2 nanoparticles' degradation efficiencies were determined from Rh-B dye under visible light irradiation. The organic pollutants are very noxious compounds and non-degradable and produce contagious diseases, which can be remediated using a nano-photocatalyst. Activated carbon (AC) degradation is 55% due to their active sites on the activated carbon surfaces. Pure TiO2 nanoparticles decreased absorbance under light irradiation with respect to time. At 30 min intervals, pure TiO2 nanoparticles showed a 73% degradation efficiency, and their values are presented in Figure  10a. The activated carbon doping to the anatase phase increased the adsorption behaviour and decreased the dye intensity from initial dye concentrations. The decreased absorbance determined the dissociation of dye molecules. The dye molecule fragments increased due to the microporous nature of activated carbon. At 30 min intervals, activated carbondoped titanium dioxide exposed the 91% dye degradation. Anatase phase TiO2 coupled with mesoporous/microporous activated carbon exhibited enhanced degradation activity

Photocatalytic Activity
The pure AC, TiO 2 , and AC/TiO 2 nanoparticles' degradation efficiencies were determined from Rh-B dye under visible light irradiation. The organic pollutants are very noxious compounds and non-degradable and produce contagious diseases, which can be remediated using a nano-photocatalyst. Activated carbon (AC) degradation is 55% due to their active sites on the activated carbon surfaces. Pure TiO 2 nanoparticles decreased absorbance under light irradiation with respect to time. At 30 min intervals, pure TiO 2 nanoparticles showed a 73% degradation efficiency, and their values are presented in Figure 10a. The activated carbon doping to the anatase phase increased the adsorption behaviour and decreased the dye intensity from initial dye concentrations. The decreased absorbance determined the dissociation of dye molecules. The dye molecule fragments increased due to the microporous nature of activated carbon. At 30 min intervals, activated carbon-doped titanium dioxide exposed the 91% dye degradation. Anatase phase TiO 2 coupled with mesoporous/microporous activated carbon exhibited enhanced degradation activity compared to pure TiO 2 nanoparticles. The C/C 0 spectrum demonstrated the degradation rate of pure TiO 2 and AC/TiO 2 nanoparticles, as shown in Figure 10c. The rate of degradation evaluation using pseudo-first-order kinetics and their calculated values are displayed in Figure 10c. Comparatively, anatase TiO2 nanoparticles revealed minimal degradation activity for 30 min (73%) compared to AC/TiO2 nanoparticles (91%), confirming the high number of productions. The wide bandgap photocatalyst does not give better adsorption in visible light regions, which is overcome by doping of activated carbon. The photocatalytic mechanism of AC/TiO2 nanoparticles is presented in Figure 10d, and their steps are as follows:

Rh-B + ·OH and O2˙− → CO2 + H2O + by-products---5
The formation of activated carbon and titanium dioxide nanoparticles is based on the work functions. The excited electrons are transferred from lower work functional material to higher work function materials which establish the Schottky barrier. The light entry increased the formation of e-h pairs [63,64]. The activated carbon reduced the bandgap and suppressed recombination, allowing excited electrons to move from the valence to Comparatively, anatase TiO 2 nanoparticles revealed minimal degradation activity for 30 min (73%) compared to AC/TiO 2 nanoparticles (91%), confirming the high number of productions. The wide bandgap photocatalyst does not give better adsorption in visible light regions, which is overcome by doping of activated carbon. The photocatalytic mechanism of AC/TiO 2 nanoparticles is presented in Figure 10d, and their steps are as follows: AC/TiO 2 + hν → e − (C.B) + h + (V.B) The formation of activated carbon and titanium dioxide nanoparticles is based on the work functions. The excited electrons are transferred from lower work functional material to higher work function materials which establish the Schottky barrier. The light entry increased the formation of e-h pairs [63,64]. The activated carbon reduced the bandgap and suppressed recombination, allowing excited electrons to move from the valence to the conduction bands. The free holes in the conduction band were engaged with the excited electrons [65,66]. This process is delayed by the doping of activated carbon. Furthermore, the deduction of recombination generated superoxide radicals and hydroxyl radicals. The above-mentioned productions help to convert the dye compounds to small noxious-free molecules. The photocatalytic degradation is influenced by holes and superoxides, and free radicals. Moreover, it can be responsible for efficient catalytic activity. The quenching experiment is displayed in Figure 11. The withoutquenchers degradation percentage is 91%, and it can compare with holes, superoxides, and hydroxide suppression values. The figure presents the suppression values of IPA < BQ < TEOA for hydroxide < superoxides < holes, respectively. The holes' degradation endurance is better than the hydroxide and superoxide degradation efficiency, and their association with the photocatalyst improved the photocatalytic dye degradation activity. Based on the obtained findings, AC/TiO 2 nanoparticles demonstrated a high absorption capability and enriched the degradations.
Catalysts 2022, 12, x FOR PEER REVIEW 13 of 16 the conduction bands. The free holes in the conduction band were engaged with the excited electrons [65,66]. This process is delayed by the doping of activated carbon. Furthermore, the deduction of recombination generated superoxide radicals and hydroxyl radicals. The above-mentioned productions help to convert the dye compounds to small noxious-free molecules. The photocatalytic degradation is influenced by holes and superoxides, and free radicals. Moreover, it can be responsible for efficient catalytic activity. The quenching experiment is displayed in Figure 11. The without-quenchers degradation percentage is 91%, and it can compare with holes, superoxides, and hydroxide suppression values. The figure presents the suppression values of IPA < BQ < TEOA for hydroxide < superoxides < holes, respectively. The holes' degradation endurance is better than the hydroxide and superoxide degradation efficiency, and their association with the photocatalyst improved the photocatalytic dye degradation activity. Based on the obtained findings, AC/TiO2 nanoparticles demonstrated a high absorption capability and enriched the degradations. Figure 11. Quenching experiment.

Conclusions
The zapota leaf extract was used to prepare activated carbon doping titanium dioxide nanoparticles. The production of nanophase particles in a sustainable way reduced environmental risk and encouraged green calmness in the environment. The heterogeneous photocatalytic material of activated carbon-doped titanium dioxide nanoparticles entered/modified the TiO2 lattice system and assisted the lattice distortions and reduction in the bandgap, enhanced the surface morphology, and created C-Ti-O formations. The activated carbon entry increased the visible light adsorption and generated the super oxide ions and hydroxyl radical on the surfaces. Reduced e-h pairs and carrier migrations increased the photocatalytic activity against Rh-B dye in AC/TiO2 (91%) compared to TiO2 (73%) nanoparticles. The bacterial investigation of S. aureus and E. coli against TiO2 and AC/TiO2 nanoparticles established the bacterial denaturation of the nanoparticles. E. coli bacteria are more active than S. aureus in the bactericidal activity of TiO2 and AC/TiO2

Conclusions
The zapota leaf extract was used to prepare activated carbon doping titanium dioxide nanoparticles. The production of nanophase particles in a sustainable way reduced environmental risk and encouraged green calmness in the environment. The heterogeneous photocatalytic material of activated carbon-doped titanium dioxide nanoparticles entered/modified the TiO 2 lattice system and assisted the lattice distortions and reduction in the bandgap, enhanced the surface morphology, and created C-Ti-O formations. The activated carbon entry increased the visible light adsorption and generated the super oxide ions and hydroxyl radical on the surfaces. Reduced e-h pairs and carrier migrations increased the photocatalytic activity against Rh-B dye in AC/TiO 2 (91%) compared to TiO 2 (73%) nanoparticles. The bacterial investigation of S. aureus and E. coli against TiO 2 and AC/TiO 2 nanoparticles established the bacterial denaturation of the nanoparticles. E. coli bacteria are more active than S. aureus in the bactericidal activity of TiO 2 and AC/TiO 2 nanoparticles. Furthermore, according to the results of the characterization, TiO 2