1 Introduction

One of the promising approaches to address the environmental and energy crises includes the efficient and affordable conversion of solar energy to chemical energy [1, 2]. Coinciding with this principle of sustainable chemistry; photocatalysis can secure a potential path toward solar energy conversion [3]. Photocatalysis can secure the opportunity to harness plentiful and clean solar energy through practical technology [4,5,6]. The landmark publication on photo-electrochemical technology sparked significant research interest in using semiconductor photocatalysts for wastewater treatment [4, 7,8,9]. However, the majority of investigated photocatalysts include wide band-gap semiconductors (such TiO2 and ZnO); they expose photo-catalytic activity when exposed to UV light. TiO2 NPs are employed for degradation of organic contaminants [10, 11]. Moreover, TiO2 is a potential semi-conducting materials for solar cell applications due to its high chemical stability, low toxicity [12, 13]. Furthermore, TiO2 NPs are widely employed as photo-anode materials due to their high UV light absorption, good chemical solubility, superior corrosion resistance [14, 15]. Since UV light contributes to only 4% of the entire solar spectrum; this significantly hinders the practical use of wide band-gap semiconductors [16, 17].

Semiconductor photocatalysts can absorb photons with energies equal to or greater than their band-gap energy [18, 19]. The VB develops positive holes because of the photoexcitation of its electrons to the CB. Then the electron acceptors or electron donor species are reduced or oxidized at catalytic active spots on the semiconductor surface; consequently photocatalytic redox reactions could take place [20]. The photocatalytic reaction over semiconductor surface could be less effective due to the deactivation process of electron–hole pair re-combination. Therefore, the photocatalytic processes should speed up the separation and migration of the photogenerated electron–hole pairs to prevent their re-combination [21].

Recent advances in ZnO-based photocatalysts for water treatment technologies were reviewed by Lee et al. [22]. It was widely accepted that suitable architecture with a minimum amount of electron loss during the excitation stage and a maximum amount of photon absorption was necessary for the efficacy of ZnO photocatalyst in heterogeneous photocatalytic reactions [23].

Anatase offers a fresh starting point for the development of novel solar energy harvesting materials. The number of publications on photocatalysis has increased significantly since 2010, after the first report on TiO2-based photocatalysts [24].

Nowadays, there has been an increase in research focused on the formation of new, effective photocatalysts. To extend the light absorption over the UV–Vis range, the combination of wide band-gap semiconductor photocatalysts with noble metals demonstrated promising features [25, 26]. The main role of transition metals is to act as dopant in an attempt to enhance the efficiency of electron–hole pair separation, and to extend the lifetime of charge carriers [27, 28]. Silver has attracted considerable attention as silver particles could act as electron trap that could prevent photo-generated charge carrier re-combination and could facilitating electron excitation via created local electrical field [29]. Nobel metals were found to be an efficient dopant in TiO2 thin films [30].

Ground and surface water contamination by industrial dyes is a real threat to human health and living organisms. Synthetic dyes are widely used in textile and paper industry, leather manufacturing, plastics, cosmetics, rubber industries, and printing [31]. Basic Fuchsine (BF) dye is one of the most significant triphenylmethane dyes in textiles, ink, and leather industries. Its introduction into the environment is not only hazardous to aquatic life, but also carcinogenic to humans and animals [32]. Synthetic dyes removal from wastewater is an environmental challenge [2, 32, 33]. Thus, removal of BF is a great challenge for water purification and conservation [20].

In this work, titanium dioxide nanoparticles were developed via facile hydrothermal synthesis. Nobel metal deposition was conducted to develop high quality Ag–TiO2 and Ni–TiO2 nanocomposites. The developed heterogeneous photocatalysts were employed for wastewater treatment. Ag–TiO2 nanocomposite demonstrated superior photocatalytic activity under ultraviolet, and visible region. This superior performance was attributed to the deposited Ag metal. The effect of solution pH, photocatalyst dosage, dye initial concentration, and H2O2 addition on the degradation efficiency was also investigated and optimized.

2 Materials and methods

2.1 Chemicals

Anatase nanoparticles (NPs) were developed via hydrothermal synthesis. The adopted titanium salt precursor was an aqueous solution 50 wt% of titanium IV bis (ammonium Lactato) di hydroxide (TIBALD). Hydrogen peroxide (H2O2, 30 vol%) was employed for OH− ions during hydrothermal synthesis. Silver nitrate, and nickel nitrate (Aldrich, 99.99%) were employed as the precursor for nobel metal dopant. Basic Fuchsine (a fluorescent dye composed of rosaniline, magenta II, pararosaniline, and new fuchsine, Aldrich, <  = 100%) was employed as a contaminant. The chemical structure of BF dye is represented in Fig. 1. All chemicals were used as perceived without further treatment.

Fig. 1
figure 1

The chemical structure of Basic Fuchsine dye

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2.2 Nanoparticle synthesis

2.2.1 Synthesis of anatase nanoparticles

Colloidal anatase (TiO2) particles with consistent product quality were fabricated sustainably via established continuous hydrothermal processing (Fig. 2).

Fig. 2
figure 2

Flow diagram of continuous hydrothermal synthesis system

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Where super-critical water (Flow A) at 225 bars and 415 ℃ (20 ml/min) was pumped down against an up flow of cold metal salt (Flow B) (0.05 M TIBALD) at 245 bars and 20 ℃ (10 ml/min.). NPs were formed at the border of the two fluids inside the counter reactor (C). The fabricated anatase NPs were cooled down before collection point (E).

2.2.2 Synthesis of anatase-based nanocomposite

The synthesized colloidal anatase (TiO2) nanoparticles were collected from the medium in which they were produced and then dispersed again in noble metal nitrate solution (silver, nickel) using an ultrasonic bath for 1 h. The weight percentage of noble metal ions (Ag+, Ni+) to anatase was 1:9. Sodium borohydride was employed as a reducing agent. The stoichiometric ratio of sodium borohydride to noble metal ions (Ag+, Ni+) was 3:1. The reduction of noble metal was conducted under vigorous magnetic stirring for 30 min, to ensure optimal homogeneity and even deposition of the noble metal on TiO2 surface.

2.3 Nanoparticle characterization

The morphology and elemental mapping of synthesized Ag–TiO2, and Ni–TiO2 were determined by SEM (JWEL JSM 6010 LA, Japan) equipped with EDAX detector (X-act, Oxford instruments). The crystalline structure of TiO2, Ag–TiO2, Ni–TiO2 were assessed using XRD; the diffraction pattern was collected using a Siemens D-5000 powder X-ray diffractometer. The chemical bonding and elemental analysis of Ag–TiO2 and Ni–TiO2 nanocomposites were determined by X-ray photoelectron spectroscopy (XPS) Thermo Scientific K-Alpha ESCA instrument.

2.4 Photocatalytic degradation of basic fuchsine (BF)

TiO2, Ag–TiO2, and Ni–TiO2 NPs (10 mg) were mixed with 50 ml of BF solution in separate 125 ml beakers with initial concentration C0 = 20 ppm, 25 ℃ for 90 min in the dark, until adsorption–desorption equilibrium was reached. The activity of anatase-based nanocomposites was measured for the degradation of BF under both UV and visible light irradiation in separate experiments. The used UV reactor was cylindrical shape having dimensions of 27 cm length, 2.5 cm diameter. The source of UV light is a 10 W high pressure mercury lamp (wavelength 254 nm). On the other hand, the photo-reactor was irradiated by a visible lamp composed of 52 white light LEDs (nominal power: 55 W) with wavelength emission in the range 400–800 nm surrounded by aluminum reflectors to minimize irradiation loss. The lamp was positioned at the top; the distance between the light source and the reactor was 10 cm. A sample of the BF suspension (1 ml) has been collected using a syringe fitted with a filter (2.5 mm pore size) at regular time intervals of irradiation. The degradation rate of BF was determined by analyzing the changes in BF concentration over time using UV–Vis spectrophotometer (Agilent Technologies Cary 60 UV–Vis), at maximum absorption wavelength (λ max) of 546 nm. Deionized water was utilized as a reference solution [34].

3 Results and discussions

3.1 Characterization of nanoparticles

The fabricated anatase (TiO2) NPs demonstrated mono-dispersed particles of 5 nm average particle size. TEM micrographs demonstrated high-quality particles with uniform particle sizes as illustrated in Fig. 3.

Fig. 3
figure 3

TEM micrographs of synthesized anatase (TiO2) nanoparticles

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XRD pattern confirmed high-quality anatase crystalline structure. Sharp and intense peaks were observed at 2Ɵ = 25.281° (101), 37.801° (004), 48.050° (200), 55.062° (211), and 62.690° (204). XRD peaks were found to be identical with ICCD card no. 00–021-1272 [35]. Ag–TiO2 experienced intense characteristic peaks of silver at 2Ɵ = 38.117°, 44.279°, 64.428°, and 77.475° corresponding to (111), (200), (220), and (311) respectively. Silver peaks were found to be in good accordance with ICCD card no. 00–004-0783. It can be assumed that silver NPs were effectively deposited on the surface of TiO2 NPs (Fig. 4a). The XRD pattern of Ni–TiO2 was investigated to virgin TiO2. XRD diffractogram of Ni–TiO2 demonstrated XRD diffractogram similar to TiO2. Even though deposited nickel demonstrated a complete change of TiO2 from white to yellowish green. The main nickel signals at 2Ɵ = 44.508, 51.8472, and 76.372, corresponding to (111), (200), (220), and (311) respectively, were not observed; this can be ascribed to the low XRD signature of nickel to that of TiO2 (Fig. 4b).

Fig. 4
figure 4

XRD diffractogram of Ag–TiO2 (a), Ni–TiO2 (b) nanocomposite to virgin TiO2

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The dispersion and quantification of deposited nobel metal particles were investigated using SEM. EDAX micrographs of Ag–TiO2 nanocomposite demonstrated uniform deposition of silver metal (Fig. 5a). Ni–TiO2 nanocomposite demonstrated uniform dispersion of nickel particles on the surface of TiO2 particles (Fig. 5b).

Fig. 5
figure 5

Elemental mapping of Ag–TiO2 (a), Ni–TiO2 (b) nanocomposite

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The quantification of deposited nobel metals was evaluated via EDAX detector. While Ag–TiO2 nanocomposite demonstrated silver content of 2.33 at% (Fig. 6a); Ni–TiO2 nanocomposite demonstrated nickel content of 2.59 at% (Fig. 6b).

Fig. 6
figure 6

Elemental composition of Ag–TiO2 nanocomposite (a), Ni–TiO2 nanocomposite (b)

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Elemental analysis as well as binding energy was investigated using XPS analysis. Precise elemental binding energies (BE) were determined to carbon C1s peak at 284.8 eV. XPS spectroscopy was employed to identify and quantify the elements in the sample. Deposited nobel metals nickel and silver were identified via the binding energy of Ni2P and Ag3D respectively (Fig. 7).

Fig. 7
figure 7

XPS survey spectra of Ag–TiO2, Ni–TiO2 nanocomposite

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Survey spectra offered the determination of the elemental composition of Ag–TiO2, and Ni–TiO2 nanocomposite (Table 1).

Table 1 Elemental composition of Ag–TiO2, and Ni–TiO2 nanocomposites
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Ag–TiO2 sample demonstrated a similar value of O/Ti to virgin TiO2; this indicates that the deposited silver is in the metallic form. The analysis of the oxidation state of silver relies on the position of auger lines which makes it possible to determine the chemical environment of silver. Values of Auger parameter allow us to determine the chemical environment of silver [36, 37]. The auger parameter of Ag–TiO2 demonstrated value of 726.03 which corresponds to Ag (0) (Fig. 8).

Fig. 8
figure 8

Auger parameter for Ag element in Ag–TiO2 nanocomposite

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The values of Ag3d binding energy as well as Auger Parameter value are tabulated in Table 2.

Table 2 Silver Ag3d binding energy and Auger Parameter
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Auger parameter confirmed XPS survey spectra and O/Ti ratio. Auger parameter confirmed the successful deposition of the silver element on the surface of TiO2. Ni–TiO2 nanocomposite experienced an increase in O/Ti ratio; the deposited nickel could be partially in the form of oxide or hydroxide. This feature was further investigated via the binding energy of Ni2P (Fig. 9).

Fig. 9
figure 9

The binding energy of Ni2P of Ni–TiO2 nanocomposite

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Ni2P3/2 demonstrated three peaks fitting correspond to nickel hydroxide. The binding energy of Ni2P3/2 of the center of gravity for Ni2P3/2 demonstrated 856.57 eV; this value is slightly higher than that corresponding to Ni (OH)2 compound of 855.8 eV. It can be concluded that the deposited nickel is a hybrid of nickel and nickel hydroxide [38].

The impact of deposited noble metal on lattice oxygen binding energy was investigated via O1S scan. O1S binding energy of Ni–TiO2, and Ag–TiO2 was investigated to virgin TiO2. Whereas virgin TiO2 demonstrated O1S binding energies corresponding to oxide lattice (A), O–H surface (B), and organic hydrocarbon (C). Deposited nickel was found to increase the atomic percent of both O1S (B), and O1S (C); this can be ascribed to the fact that the deposited nickel is a combination of Ni, and Ni(OH)2. On the other hand, the deposited silver was found to eliminate O1S (C) of high binding energy and increase the O1S (A) and O1S (B). This indicates that the deposited silver is in zero valence state Ag(0) [39]. The Quantification of O1S binding energies and relative percentages are tabulated in Table 3.

Table 3 O1S Binding energies and at% of TiO2, Ni–TiO2, and Ag–TiO2
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It is obvious that the deposited Ag (0) eliminated O1S (C) of high binding energy; in the meantime, it offered high percentages of low binding energy O1S. This can offer novel catalyzing ability. The spectra of O1S scan for investigated samples are represented in Fig. 10.

Fig. 10
figure 10

O1S spectra for: anatase TiO2 (a), Ni–TiO2 (b) Ag–TiO2 (C)

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It is obvious that silver particles eliminated the hydrocarbon oxygen of high binding energy and offered an increase in lattice and hydroxyl oxygen of low binding energy. This could offer novel photocatalytic properties. These findings could demonstrate the surge of O/Ti value for Ni–TiO2 sample.

3.2 Analysis of optical properties

The analysis of diffuse reflectance was performed using a Perkin Elmer UV–visible spectrophotometer to determine the absorption peaks and bandgap energies of the Ni–TiO2 and Ag–TiO2 nanoparticles. The absorption and reflectance maxima of surface plasmons were acquired and depicted in Fig. 11. The findings indicate that the optical characteristics of the specimens vary depending on the type of doping. The observed phenomenon can be attributed to the plasmon resonance effect exhibited by Ag–TiO2 and Ni–TiO2 nanoparticles [40,41,42]. These nanoparticles possess a collective oscillation of their outermost electrons and can absorb visible light [43]. To assess the optical band-gap energy of the Ag–TiO2 and Ni–TiO2 NPs samples, the Kubelka–Munk algorithm, F(R) = (1 − R)2/2R, was utilized [44]. Where R stands for reflectance and F(R) represents the amount of absorption. The optical band gap energy for the Ag–TiO2 and Ni–TiO2 NPs are tabulated in Table 4 and represented in Fig. 11. It is obvious that anatase based nanocomposite samples demonstrated two band gaps, due to the existence of two phases [44]. This finding was found to be in good accordance with XRD data; furthermore, the synergistic effect between TiO2 and noble metals (Ag and Ni) could decrease the band gap energy.

Fig. 11
figure 11

Kubelka–Munk plots of samples displaying the bandgap energies of a Ni–TiO2, and b Ag–TiO2

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Table 4 The optical band gap energies
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3.3 Removal performance of Ag–TiO2 and Ni–TiO2 NPs toward (BF) dye

The removal of BF was measured at λmax = 546 nm and the calibration curve of BF was done using serial dilution (2.5, 5, 10, 15, and 20 ppm) of BF as demonstrated in Fig. 12 [45].

Fig. 12
figure 12

UV–Vis. A spectrum of Basic fuchsine (BF) and calibration curve at different concentrations of BF

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This material possesses the potential to act as a carcinogen and has the capacity to induce irritation, dermatitis, and conjunctivitis. The act of consuming a substance has the potential to induce irritation in the gastrointestinal tract, leading to symptoms such as nausea, vomiting, and diarrhea [46,47,48]. Therefore, BF was chosen as a model contaminant to evaluate the photocatalytic activity of the synthesized photocatalysts. Comparative investigation for different dye removal aspects including adsorption, photocatalysis using UV irradiation, and photocatalysis using visible light irradiation were evaluated for Ag–TiO2 and Ni–TiO2 to virgin TiO2.

While virgin anatase demonstrated only 10% removal via adsorption after 90 min in dark; Ag–TiO2 and Ni–TiO2 experienced removal efficiency of 20.2 and 15.9% respectively (Fig. 13a). Photocatalytic removal activity of virgin anatase under UV irradiation was limited to 43.2% after 90 min. Ag–TiO2 and Ni–TiO2 experienced removal efficiency of 54.3, and 46.8% respectively (Fig. 13b). The superior dye removal efficiency was achieved via Ag–TiO2 under visible light irradiation. Ag–TiO2 experienced dye removal of 66.8%, compared with 39.1 and 59% for virgin anatase, and Ni–TiO2 respectively as demonstrated in (Fig. 13c).

Fig. 13
figure 13

% Removal of BF within 90 min by virgin TiO2, Ag–TiO2 and Ni–TiO2, due to: a Adsorption activity in dark, b Photocatalysis under UV, and c Photocatalysis under Visible light

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3.4 Synergistic catalytic effect of Ag–TiO2 and Ni–TiO2 under UV and visible light

Following the process of adsorption, ultraviolet (UV) light was applied to the BF removal system, which included the addition of Ag–TiO2 and Ni–TiO2 as photocatalysts. The efficacy of BF removal was enhanced by up to 54.3% after 90 min when Ag–TiO2 and Ni–TiO2 were introduced into the BF solution and subjected to UV light irradiation. The analysis of the light absorption results under dark and light irradiation conditions revealed that the primary mechanism responsible for the elimination of BF was the photocatalytic degradation facilitated by the Ag–TiO2 and Ni–TiO2 nanocomposite. The maximum removal effectiveness of 54.3% was observed after a duration of 90 min. This can be attributed to the higher photon energy present in UV light and the impact of the metal–semiconductor hetero-junction created within the nanocomposite. The presence of this hetero-junction facilitates the effective separation of charges and amplifies the absorption of incident light [49].

From Fig. 13C, it is observed that Ag–TiO2 and Ni–TiO2 photocatalysts showed a unique photocatalytic activity against BF compared to virgin TiO2. Whereas Ag–TiO2 and Ni–TiO2 experienced BF removal by 66.8 and 59.0% respectively; virgin anatase demonstrated BF removal by 39.1% in 90 min under Visible light irradiation. The doping of Ag to anatase promises to generate several effects on its photocatalytic activity through the following methods. The incorporation of metal nanoparticles in photocatalysts has the potential to provide several beneficial effects. Firstly, the presence of metal nanoparticles can facilitate the separation of electrons and holes by serving as electron traps. Secondly, the introduction of metal nanoparticles can extend the absorption of light to the visible range, thereby enhancing the excitation of surface electrons through Plasmon resonances induced by visible light. Lastly, the inclusion of metal nanoparticles can bring about modifications to the surface characteristics of photocatalysts [50, 51].

It is widely accepted that the increase in photocatalytic activity by Ag dopant could be ascribed to the increase in interfacial charge transfer efficiency for TiO2, as well as enhanced charge pair separation and thereby inhibiting their recombination [52]. The photocatalytic activity by Ag–TiO2 is explained below in the mechanism section.

3.4.1 Effect of pH value on removal of BF

The pH of the solution is a crucial factor in removal studies. The impact of initial pH values of the BF solution was investigated under specific experimental conditions, including the use of 10 mg of the prepared nanocomposite, 50 ml of a 10 ppm BF solution, and a temperature of 25 °C. Figure 14a displays a graph illustrating the change in BF removal (%) over time at various solution pH levels ranging from 3.0 to 9.0. It was observed that the highest level of BF removal at equilibrium occurred at pH 9.0.

Fig. 14
figure 14

Showing a (%) removal of BF at different pH values (3.0, 5.0, 7.0 and 9.0), 50 ml Ag–TiO2 (10 mg), initial concentration of BF (10 ppm) at 25 ℃. b Point of zero charge (PZC) of Ag–TiO2

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In order to calculate the point of zero charges (PZC) of the Ag–TiO2 nanoparticles (NPs), a quantity of 0.01 g of the Ag–TiO2 NPs was mixed into a 50 mL solution of 0.01 M NaCl [53, 54]. The pH values of the solutions were modified using hydrochloric acid (HCl) or sodium hydroxide (NaOH) to achieve pH levels of 2, 4, 6, 8, 10, and 12. The samples were subjected to agitation at a speed of 200 revolutions per minute (rpm) for 48 h. The pH values of the solutions were determined after the separation of (Ag–TiO2 nanoparticles). The determination of the pH at the point of zero charge (PZC) was accomplished via a graph illustrating the relationship between the final pH and the initial pH. Based on the data presented in Fig. 14b, it can be observed that the (PZC) corresponds to the pH value at which there is negligible difference between the final and initially measured pH values. The PZC was found to be at pH 6.75. This means that the surface charge of the photocatalyst, specifically the Ag–TiO2 nanoparticles, exhibits positive charge when the pH is below the PZC, and negative charge when the pH is above the PZC. Moreover, in cases where the pH of the solution equals the pH of the PZC, the surface charge of the photocatalyst becomes neutral, resulting in a low electrostatic force between the photocatalyst surface and ions (specifically BF ions) [55,56,57]. This result explained the reason for the observed maximal photocatalytic degradation of BF at pH 9.0, as depicted in Fig. 14a. Therefore, it can be concluded that the net surface charge of the Ag–TiO2 nanoparticles is negative, resulting in an attraction towards the positive charge of BF. This interaction ultimately enhances the photocatalytic degradation of BF [58]. The degradation of BF during photocatalysis demonstrated decrease as the pH reached 5.0. This phenomenon can be attributed to the positive net surface charge of the Ag–TiO2 nanoparticles, which leads to repulsion forces between the positive charge of BF and the positive net surface charge of the Ag–TiO2 nanocomposite. This positive net surface charge is observed at pH levels below 6.2.

In general, the solution pH significantly impacted the photocatalytic degradation rate of pollutants. Anatase, under UV light irradiation, generates electron–hole pairs. Holes react with water to produce hydroxyl radicals (OH•), powerful oxidants that degrade pollutants. At acidic pH (pH < 7), protonation of surface hydroxyl groups (TiOH) to create TiOH2+, could enhance hole capture and OH• generation. Increased OH• radicals could lead to fast degradation rates at optimal pH. At basic pH (pH > 7), De-protonation of TiOH to TiO− could reduce hole capture and OH• generation. Low OH• could result in slow degradation rates. Overall: Anatase TiO2 exhibits a bell-shaped curve for degradation rate constants with respect to pH, peaking at an optimal pH (usually around 3–5). Silver dopant could introduce additional energy levels within the band gap of TiO2. This could facilitate visible light absorption and charge separation and could boost photocatalytic activity [59]. Silver dopant demonstrated shift in the optimal pH range for maximum degradation rate compared to un-doped TiO2. The shift depends on the doping level, silver distribution, and the target pollutant [60]. Doping might influence surface properties and adsorption behavior of pollutants, affecting the pH dependence. The influence of pH on silver-doped TiO2 can be much complex due to the interplay of various factors [61].

3.4.2 Effect of initial concentration of BF and amount of Ag–TiO2 nanocomposite

The impact of ionic strength on the removal process was investigated by varying the starting concentration of BF while maintaining all other reaction conditions constant. Figure 15a demonstrates the relationship between the percentage of elimination and the contact time for various initial BF concentrations (5.0, 10.0, and 15.0 ppm).

Fig. 15
figure 15

Effect of initial concentration of BF (5, 10, 15) ppm (a), and photocatalyst dose on the removal efficiency of BF (50 ml BF solution (10 ppm) (b), Temp. = 25 ℃ and pH 9)

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The results indicate that the efficiency of degradation has an inverse relationship with the concentration of BF. Particularly, the produced nanocomposite demonstrates the capability of effectively degrading BF, even when present at high initial concentrations, under visible light irradiation.

The impact of different nanocomposite doses on the removal efficacy of BF under visible light was assessed. The amount of the photocatalyst used was varied at 5, 10, and 20 mg, while maintaining a constant concentration of BF at 10 ppm, as depicted in Fig. 15b. The findings of the study demonstrated a positive correlation between the dosage of the photocatalyst (ranging from 5 to 20 mg) and the efficiency of pollutant removal. The observed correlation between the increase in removal efficiency and the amount of photocatalyst could be attributed to the increase in the available active area or active sites of the photocatalyst to volume ratio of the BF solution [18, 62]. TiO2@Ag3 composite exhibited superior photocatalytic performance with removal efficiency of 97% compared with 77% for TiO2 against Rhodamine B dye [63]. Doping with Ag was beneficial to provide efficient separation of the photogenerated electron–hole and interface charge transfer [64].

The dependence of photo-catalytic degradation reaction rate constants on the catalyst dose can differ significantly between pristine anatase and its silver-doped counterpart. Pristine anatase demonstrated an increase in the reaction rate with increase in catalyst doze; this can be ascribed to the larger number of available active sites on the catalyst surface [65]. However further increases in TiO2 dose can lead to a decrease in reaction rate constants; this can be attributed to several factors such as light shielding, excess catalyst particles can block light from reaching the active sites within the reaction mixture, hindering photoexcitation and radical generation [66]. Increase in catalyst concentration could promote particle aggregation, reducing their effective surface area and accessibility to reactants. High catalyst density can facilitate recombination of photogenerated electron–hole pairs, thereby reducing the efficiency of charge separation and radical formation [67].

Silver-doped TiO2 demonstrated enhanced visible light absorption: silver dopant could introduce new energy levels within TiO2 bandgap, allowing it to absorb visible light, potentially leading to higher reaction rates under broad light spectra [68]. Plasmonic effect, depending on the specific silver distribution and morphology, plasmonic resonance can enhance the local electric field at the catalyst surface, potentially promoting charge separation and improving photocatalytic activity [69]. Generally, the optimal catalyst dose for Silver-doped TiO2 might be lower compared to pristine TiO2 due to potential light-shielding and deactivation concerns [70].

3.4.3 Kinetic studies

The degradation rate of BF can be calculated using the following equation:

$$- \ln \, C_{t} /C_{0} = - Kt$$
(1)

where Ct and C0 are the remaining and the initial concentrations (ppm) of BF respectively, while t is the removal time (min) and k represents the removal rate constant (min−1) [33, 71,72,73]. Figure 16a. shows a relation of − ln Ct/C0 vs. t.

Fig. 16
figure 16

a Pseudo-first-order reaction model for Basic fuchsine degradation under UV light irradiation and 10 mg nanocatalyst, 50 mL of 5, 10, and 15 ppm BF concentration, b The relation of apparent pseudo-first-order rate constants vs. initial concentration of BF

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The results indicated that the kinetics of the removal reaction followed rate laws that can be approximated as pseudo-first order. Furthermore, as seen in Fig. 16b, it can be observed that an elevation in BF concentration results in a reduction of the apparent pseudo-first-order rate constants. The dependence of reaction rate constants on the concentration of BF is consistent with the findings reported in the existing literature [58, 74]. The relationship between the concentration of Basic Fuchsin (BF) and the photocatalytic degradation rate constant (k) is complex and can vary depending on several factors [75]. However, some general trends have been observed. As the BF concentration increases, the number of dye molecules available for interaction with the photocatalyst increases, leading to a rise in the reaction rate, and rate constant [76]. At a certain point, the available catalyst surface area becomes saturated with dye molecules, and further increase in BF concentration might not significantly affect the rate constant. However, when the BF concentration is very high, it could act as an inner filter and could impede incident light from reaching the catalyst surface. This could reduce the efficiency of photo-excitation and electron transfer, with a decrease in the degradation rate [77].

3.5 Synergistic catalytic effect of Ag–TiO2 nanocomposite with H2O2

The addition of H2O2 resulted in an enhanced photocatalytic performance of the Ag–TiO2 nanocomposite. The primary cause of this phenomenon could be correlated to the superior electron-accepting characteristics of H2O2 in comparison to molecular oxygen. This property has the potential to accelerate the rate of photocatalysis by mitigating the adverse effects of electron–hole recombination and facilitating the formation of active hydroxyl radicals [78]. It may be suggested that the observed improvement in the photodegradation of BF is attributed to the combined action of H2O2 and the synthesized photocatalysts, as depicted in Fig. 17.

Fig. 17
figure 17

% removal of Basic fuchsine by H2O2 (0, 0.1, 0.2 and 0.3%), Ag–TiO2 (10 mg) and 50 mL of 10 ppm dye concentration under visible light irradiation

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3.6 Mechanism of photocatalytic activity of Ag–TiO2 nanocomposite

Anatase is the most widely employed photocatalyst; however, its limitation is related to large ban-gap energy that limit its performance to ultraviolet (UV) light rather than visible light. This feature could restrict its practical use under visible light conditions [79]. To overcome this limitation, we have explored doping strategies, including incorporating silver (Ag) into the anatase structure. Silver dopant modified the electronic band structure of anatase TiO2, extended its absorption range into the visible spectrum [80]. Silver could introduce energy levels within the band gap, allowing the material to absorb visible light more efficiently. This enhanced light absorption ability enabled the effective utilization of solar energy for photocatalytic reactions [80]. Silver dopant could minimize the recombination of photo-induced charge carriers (electrons and holes); electrons generated by light absorption can transfer to the silver dopants, reducing the likelihood of recombination. Also, Silver dopant could induce oxygen vacancies that could act as trapping sites for charge carriers [81]. The potential mechanism can be described as follows [56, 82]. In the case of Ag–TiO2 nanocomposites acting as photocatalysts, it has been observed that when exposed to visible light, there is a transfer of electrons from the highest occupied molecular orbital (HOMO) of oxygen (O) and titanium (Ti) atoms to the lowest unoccupied molecular orbital (LUMO) of silver (Ag). The highest occupied molecular orbital (HOMO) exhibits a pronounced affinity for an additional electron to restore its equilibrium state. In the process, a single electron is acquired from a water molecule, resulting in the formation of a hydroxyl radical (·OH). The active hydroxyl (OH) radicals function as a potent oxidizing agent, effectively breaking down BF molecules to generate the ultimate oxidation products. It is important to acknowledge that the mixing of Ag–TiO2 nanocomposite with H2O2 has a synergistic impact, leading to the generation of (.OH) and HO2− radicals [56]. The cleavage of hydrogen peroxide (H2O2) catalysed by the silver-titanium dioxide (Ag–TiO2) complex can be described by the following equations, which represent two essential processes:

$${\text{Ag{-}TiO}}_{{2}} {\text{NPs + H}}_{{2}} {\text{O}}_{{2}} \to^{ + } {\text{Ag{-}TiO}}_{{2}} {\text{NPs + HO}}_{{2}}^{.} {\text{ + H}}^{ + }$$
(2)
$$^{ + } {\text{Ag{-}TiO}}_{{2}} {\text{NPs + H}}_{{2}} {\text{O}}_{2} \to {\text{Ag{-}TiO}}_{{2}} {\text{NPs + }}^{.} {\text{OH + OH}}^{ - }$$
(3)
$$\left[ 1 \right] + \left[ 2 \right]: + 2{\text{H}}_{{\text{2}}} {\text{O}}_{{\text{2}}} \xrightarrow{{{\text{Ag}} - {\text{TiO}}_{{\text{2}}} \;{\text{nanocatalyst}}}}^{{\text{.}}} {\text{OH}} + {\text{HO}}_{2}^{.} + {\text{H}}_{{\text{2}}} {\text{O}}$$
(4)

In addition to the photocatalytic activity exhibited by the Ag–TiO2 nanocatalyst, the combined action of the Ag–TiO2 nanocatalyst and H2O2 significantly enhances the overall photodegradation process by generating a greater number of active hydroxyl radicals (·OH). The potential photocatalytic mechanism is elucidated in Fig. 18.

Fig. 18
figure 18

The proposed photocatalytic mechanism of BF degradation by Ag–TiO2 nanocatalyst in the presence of H2O2

Full size image

In summary, Ag–TiO2 anatase nanocomposites exposed exciting prospects as sustainable and efficient photocatalyst, with superior performance under visible light activation. Their tunable properties and enhanced performance inherit novel features for environmental remediation and energy conversion [83].

4 Conclusion

The aim of this work was to effectively synthesize a silver-doped anatase nanocomposite for wastewater treatment. The Ag–TiO2 nanoparticles had the highest photocatalytic efficacy for BF, with a removal efficiency of 64% within a 90-min interval without H2O2. Furthermore, when combined with 0.3% H2O2 under visible light, the photocatalytic activity of the Ag–TiO2 nanoparticles increased to 88%. The Ag–TiO2 nanocomposite exhibits significant potential as a highly suitable option for the purpose of wastewater treatment. Our research offers a novel method for wastewater treatment by employing a promising nanoparticle. This strategy provides a cost-efficient solution to the urgent global water treatment issues.