Solution–Gel Method Preparation of High-Performance TiO₂/GO/CdS Nanocomposites Under Ultrasonic Radiation and Research on Antibacterial Properties

Abstract

To improve the visible-light response and antibacterial performance of titanium dioxide, a TiO₂/GO/CdS mesoporous nanocomposite was prepared via an ultrasound-assisted sol–gel method in this study. Systematic characterizations including XRD, XPS, SEM, TEM, BET, UV-Vis DRS and FTIR were carried out to analyze the structure, morphology and optical properties of the material. The results show that the composite exhibits a typical mesoporous structure with a specific surface area of 197.0962 m²/g and a pore size distribution of 2–14 nm. CdS is successfully doped into the TiO₂ matrix and forms a heterostructure with GO. UV-Vis diffuse reflectance spectra indicate that the synergistic effect of CdS and GO significantly broadens the visible-light absorption range of TiO₂ and suppresses the recombination of photogenerated carriers. Antibacterial tests using Escherichia coli as the target strain demonstrate that the TiO₂/GO/CdS composite exhibits remarkably better visible-light photocatalytic bactericidal activity than pure TiO₂ and the TiO₂/GO composite. This work provides a new strategy for the modification of TiO₂-based photocatalytic antibacterial materials, and the as-prepared composite shows promising application prospects in the antibacterial field.

1. Introduction

The fight against pathogenic microorganisms is an important issue in the protection of human life and health safety. Although antibiotics are effective in fighting germs, their misuse has led to a dwindling pool of antimicrobial drugs [1]. The ability of antimicrobial materials to inhibit certain functions of microorganisms and effectively prevent the propagation of many harmful and pathogenic microorganisms has attracted great interest from researchers. These include semiconductor photocatalytic materials [2,3], organic materials [4], metal ionic materials [5], natural biological anti-microbial materials [6] and nano carrier composites [7]. Although organic antimicrobial materials have a rapid antimicrobial effect, most of them are poor in high-temperature resistance, unstable and prone to drug resistance [8]. While metal ions such as silver, copper, and zinc have good antibacterial properties, there have been concerns about the negative effects of excessive release [9,10,11]. The performance and environmentally friendly characteristics of semiconductor photocatalytic antimicrobial materials have attracted great interest from researchers [12]. For example, titanium dioxide (TiO₂) is widely used in various fields as a safe and inexpensive antimicrobial material [13,14,15].

TiO₂ is an N-type semiconductor catalyst with relatively stable chemical and physical properties, which is non-toxic and harmless to humans [16]. The bactericidal function of TiO₂ semiconductor material is to produce a large number of electron (e⁻)/hole (h⁺) pairs under UV irradiation, and carry out redox reactions with free H₂O and O₂ in the environmental system, producing a large number of superoxide anion radicals (O₂^·−) and hydroxyl radicals (·OH) [17]. When the free radicals and bacteria come into contact with each other, the nucleic acids, enzymes and other substances in the cells are oxidized and decomposed, inhibiting the normal growth and reproduction of the bacteria in a short period of time, causing the bacteria to be damaged and eventually rupture and die [18,19]. However, the large bandgap (3.2 eV) of TiO₂ can only absorb UV light, which greatly limits the photocatalysis. Currently, metal doping is mainly done by transition and rare earth metals to reduce their bandgaps [20]. Hassan et al. synthesized Ln-doped TiO₂ nanofibers by sol–gel electrostatic spinning, where doping prevented the phase transition while reducing the bandgap [21]. Wang et al. coated TiO₂ on graphene oxide (GO) nanosheets by a solvothermal pathway, and the degradation rate of TiO₂@GO on oxytetracycline reached 89.5% under visible light [22]. In addition, decorating TiO₂ with CdS, which can reduce its charge complexation, is a good strategy [23].

Compared with multi-structured composite semiconductors, single-phase photocatalysts generally have a lower electron separation rate. Multi-structured compound semiconductors also delay the recombination of photogenerated electrons and holes to achieve enhanced photocatalytic efficiency. TiO₂/CdS photocatalytic effect was evident, along with good antimicrobial effect against Escherichia coli and positive Staphylococcus aureus [24,25]. However, the problem of electron leakage from the quantum dot/electrolyte interface into the electrolyte and complexing with holes in the electrolyte cannot be ignored [26]. The risk of introducing functional group instability and inhomogeneity cannot be avoided. Therefore, the introduction of inorganic semiconductors such as graphene oxide is a good solution to this challenge. Notably, GO can also significantly affect the photocatalytic efficiency of CdS by changing the energy band edge alignment between layers [27].

Herein, a mesoporous nano-heterojunction composite (TiO₂/GO/CdS) with a high specific surface area was obtained by utilizing a simple and efficient sol–gel method of preparation in an ultrasonic environment; the method is also reported. The amorphous TiO₂ was converted into anatase TiO₂ using high temperature. Various instrumental characterizations were performed to verify the microscopic morphology and structural composition. Its large specific surface area and particle size distribution demonstrate the porous nature. The photocatalytic lethality against Gram-negative bacteria was significantly enhanced.

2. Experimental

2.1. Materials and Regents

Tetra-n-butylorthotitanate [Ti(O-i-C₄H₉)₄] (AR, ≥98% Ti), Anhydrous ethanol (AR), Cadmium sulfide (AR, 98%), and Hydrochloride acid (AR) were purchased from Shanghai Aladdin Reagents Co., Ltd. The following reagents were obtained from their respective sources: Graphene oxide (Shanghai, China, average particle size 10 nm–20 nm); TiO₂ particles (Innochem (Beijing, China), average particle size = 25 nm). Escherichia coli, agar powder, and LB broth culture medium were supplied by the local laboratory. The materials were not subjected to any additional processing.

2.2. Synthesis

2.2.1. Synthesis of TiO₂/GO Nanocomposites

TiO₂/GO nanocomposites were synthesized by sol–gel method [28], and the preparation process is shown in Scheme 1. The pH value of 30 mL of mixed solution of anhydrous ethanol and deionized water (1:1/v:v) was adjusted to 4 with hydrochloric acid, after which GO (0.22 g) was mixed with the solution and stirred well. Tetra-n-butylorthotitanate (3.4 mL) was slowly added dropwise under vigorous stirring conditions and placed in an ultrasonic environment (45 kHz) for 5 h at 60 °C. The obtained TiO₂/GO gel was air-dried for 24 h to become solid and then dried using a vacuum drying oven (60 °C, 5 h) to remove the solvent.

To obtain anatase-type titanium dioxide nanoparticles, the above solid was calcined in a muffle furnace under argon protection at a rate of 2 °C/min (400 °C, 2 h) [29]. The product was washed 3 times with deionized water and then dried under vacuum (60 °C, 8 h) to obtain the final product.

2.2.2. Synthesis of TiO₂/GO/CdS Nanocomposites

A slight change was made from Section 2.2.1. GO was replaced with 0.44 g of a GO/CdS (1:1/wt) blend, and the rest of the steps remained unchanged. The yield of the composite product was about 58%. The structural stability and biosafety of the TiO₂/GO/CdS composite were evaluated by monitoring Cd²⁺ release during photocatalysis using inductively coupled plasma mass spectrometry (ICP-MS). The measured Cd²⁺ concentration in the reaction solution was extremely low, well below the typical environmental safety threshold. The strong interfacial interaction between CdS and the TiO₂/GO matrix effectively suppresses ion dissolution, indicating that the composite possesses good structural integrity and low ecotoxicity, and is therefore suitable for environmental purification and antibacterial applications.

2.3. Characterization

In materials analysis, the morphology and microstructure of the TiO₂/GO/CdS and TiO₂/GO were characterized by field-emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM, JEOL, JEOL-2100F, Akishima, Japan). The crystal structure, chemical compositions and chemical bonds of materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS, ESCALB MK-II, VG Instruments, Greater Manchester, UK), energy-dispersive X-ray spectroscopy (EDS, Super-X, Bruker, Billerica, MA, USA) and Fourier transform infrared spectroscopy (FTIR, VERTEX 70, Bruker). The specific surface area and particle size distribution of materials are tested by the BET (Brunauer–Emmett–Teller) method. UV-vis DRS was performed using a UV-3600 (Shimadzu Corporation, Kyoto, Japan), Lambda 750 spectrophotometer, PE (PerkinElmer, Inc., Waltham, MA, USA), and absorbance was measured using a UV-vis spectrophotometer (722, Vimipay Technology Co., Ltd., Hangzhou, China). A fluorescence spectrometer (F-4500, Hitachi, Tokyo, Japan) was used to determine the photoluminescence spectral structure and light intensity of the samples.

2.4. Antibacterial Tests

Gram-negative bacteria (E. coli) were used as target microorganisms for antimicrobial testing of all prepared materials. The original strain (100 μL) was added to a test tube containing sterile Luria–Bertani (LB) broth (35 mL) nutrient solution. The sample was incubated at 37 °C and 180 rpm in an oscillator incubator for 12 h. Subsequently, the bacterial solution was resuspended in 15 mL of 0.9% sterile NaCl solution, and the OD value of the bacterial suspension was measured at 600 nm (10⁸~10⁹ CFU/mL). The bacterial solution was diluted to 10⁵~10⁶ CFU/mL as the experimental bacterial concentration. For each photocatalytic antibacterial experiment, 5 mg of the sample was taken into a sterile test tube containing E. coli (300 μL) and sterile water (30 mL). Then, 100 µL of the solution was taken for plate coating after 4 h of incubation (37 °C, 180 rpm) under light and dark conditions, respectively. A blank control group was also set up as a comparison. Finally, the solid medium was incubated in a sterile incubator (37 °C) for 24 h to count the number of colonies. All antimicrobial experiments were performed in triplicate. The survival rate of bacteria S (%) was used to assess the antimicrobial capacity of the materials. The survival rate is defined as follows:

$$S={\displaystyle \frac{N}{M}} \times 100\%$$

(1)

where M (CFU/mL) is the number of colonies in the blank control group and N (CFU/mL) is the number of colonies after treatment with the material under visible light and dark conditions.

3. Results and Discussion

Figure 1 presents the nitrogen adsorption–desorption isotherms, pore size distribution, and XRD patterns of the two composite materials. As shown in Figure 1a, both isotherms exhibit typical type IV characteristics of mesoporous materials with a distinct H3 hysteresis loop in the high-pressure region (P/P₀ > 0.8), indicating the presence of slit-shaped mesopores. The adsorption quantity of TiO₂/GO/CdS is higher, corresponding to a specific surface area of 197.0962 m²/g, which is significantly larger than that of TiO₂/GO, suggesting that CdS doping leads to a more developed pore structure and provides more active sites for photocatalytic reactions. Figure 1b reveals that the pore sizes of both materials are mainly distributed in the range of 2–14 nm (20–140 Å), with a slightly larger pore volume observed for TiO₂/GO/CdS, confirming its richer mesoporous structure [30,31]. In Figure 1c, both samples show characteristic diffraction peaks of TiO₂ (marked by ♦), while additional peaks corresponding to CdS (marked by ▼) appear at 25°, 42°, etc., in the TiO₂/GO/CdS pattern, verifying the successful incorporation of CdS into the TiO₂/GO matrix without destroying the crystal structure of TiO₂, laying a structural foundation for the subsequent improvement of photocatalytic and antibacterial performance.

Figure 2 presents the X-ray photoelectron spectroscopy (XPS) characterization results of the two composite materials, revealing their elemental composition and chemical states comprehensively. The survey spectrum in Figure 2a shows that the TiO₂/GO sample exhibits characteristic peaks of Ti 2p, O 1s, and C 1s, while the TiO₂/GO/CdS sample displays additional Cd 3d and S 2p peaks, directly confirming the successful incorporation of CdS into the TiO₂/GO matrix. The high-resolution Ti 2p spectrum in Figure 2b reveals two typical peaks of Ti⁴+ for both samples: Ti 2p_3/2 (~463.8 eV) and Ti 2p_1/2 (~457.8/458.1 eV), with a slight shift after CdS modification, indicating electronic interactions between CdS and the TiO₂/GO framework. The S 2p spectrum in Figure 2c shows a characteristic peak at 160.48 eV corresponding to S²⁻, and the Cd 3d spectrum in Figure 2d exhibits two distinct peaks at 411.14 eV (Cd 3d_5/2) and 404.34 eV (Cd 3d_3/2), further verifying the presence of CdS. The O 1s spectrum in Figure 2e can be deconvoluted into lattice oxygen (~529.4/529.0 eV), hydroxyl oxygen (~531.3/531.5 eV), and adsorbed oxygen (~532.6/532.9 eV), with a blue shift in the hydroxyl oxygen peak after CdS doping, reflecting changes in the surface chemical environment. The C 1s spectrum in Figure 2f can be fitted into C-C/C=C (~284.2 eV), C-O (~285.7/285.1 eV), and C=O (~288.3/288.1 eV), retaining the typical functional groups of GO and indicating that the composite process does not destroy the GO structure [32,33,34,35]. Overall, the XPS results fully validate the elemental composition and chemical states of the TiO₂/GO/CdS composite, providing direct surface chemical evidence for understanding the enhanced photocatalytic and antibacterial performance.

Figure 3 shows the SEM morphology and EDS elemental mapping/quantitative analysis of the TiO₂/GO mesoporous composite. The SEM images in (a) and (b) reveal that the material is composed of densely aggregated TiO₂ nanoparticles with a size of approximately 50–100 nm, forming abundant mesoporous channels between particles, which is consistent with the previous BET results and provides sufficient active sites and mass transfer pathways for photocatalytic reactions [36,37,38]. The subsequent EDS elemental mapping clearly demonstrates the uniform distribution of C, O, and Ti elements: C corresponds to the GO matrix, while O and Ti originate from the TiO₂ component, with no obvious elemental segregation, indicating excellent interfacial compatibility between TiO₂ and GO. The EDS spectrum and quantitative analysis confirm that the composite is mainly composed of O, Ti, and C, with trace amounts of S and Cd detected. Analysis of the binary TiO₂/GO sample unexpectedly shows trace signals of S and Cd. These elements are not expected from the nominal synthesis, which used only GO and titanium tetra-n-butoxide. The most plausible source of the sulfur signal is residual sulfate or sulfonate groups that remain in the GO from its preparation by the Hummers’ method, where concentrated H₂SO₄ is used, and subsequent washing may not remove all sulfur-containing species. The trace Cd could originate from incidental contamination—for example, from shared glassware, the furnace, or from reagents that contain cadmium as a low-level impurity—because Cd was not intentionally introduced at this stage. Overall, the SEM and EDS results visually present the nanoporous morphology and homogeneous elemental distribution of the TiO₂/GO composite, verifying its mesoporous structure and component uniformity, and laying a reliable morphological and compositional foundation for subsequent CdS modification and photocatalytic performance studies [39,40,41].

Figure 4 presents the SEM morphology and EDS elemental mapping/quantitative analysis of the TiO₂/GO/CdS mesoporous composite. The SEM images in (a) and (b) reveal that the material consists of densely aggregated nanoparticles with a size of approximately 50–100 nm, retaining abundant mesoporous channels between particles, which aligns with the previous BET results and provides sufficient active sites and mass transfer pathways for photocatalytic reactions. The subsequent EDS elemental mapping clearly demonstrates the uniform distribution of five elements: C, Ti, O, Cd, and S, where C corresponds to the GO matrix, Ti and O originate from the TiO₂ component, and Cd and S correspond to the CdS component, with no obvious elemental segregation [42,43,44], indicating excellent interfacial compatibility among TiO₂, GO, and CdS. The EDS spectrum and quantitative analysis further confirm that the composite is mainly composed of Ti, O, C, Cd, and S, with element contents matching the designed composition, verifying the successful incorporation of CdS. Overall, the SEM and EDS results visually present the nanoporous morphology and homogeneous elemental distribution of the TiO₂/GO/CdS composite, verifying its mesoporous structure and component uniformity, and laying a reliable morphological and compositional foundation for subsequent photocatalytic and antibacterial performance studies [45,46,47,48]. EDS analysis of the binary TiO₂/GO sample unexpectedly detected trace signals of S and Cd. These elements were not intentionally introduced at this stage. The most plausible source of sulfur is residual sulfate or sulfonate groups originating from the graphene oxide synthesis (e.g., from H₂SO₄ used in the Hummers’ method), which may not have been completely removed by washing. The trace Cd signal is likely due to incidental contamination, possibly from shared glassware, the calcination furnace, or low-level impurities in reagents. Importantly, these signals do not compromise the conclusion that CdS was successfully incorporated only in the ternary composite.

Figure 5 presents the transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) characterization results of the TiO₂/GO mesoporous composite. TEM images (a–d) at different magnifications reveal that the material is composed of densely aggregated TiO₂ nanoparticles with a size of approximately 10–50 nm, forming continuous mesoporous channels between particles, which is consistent with previous BET and SEM results and provides abundant active sites and efficient mass transfer pathways for photocatalytic reactions. HRTEM images (e–f) display clear lattice fringes with a d-spacing matching the (101) crystal plane of anatase TiO₂, confirming the anatase crystalline phase of TiO₂. Meanwhile, thin GO sheets are observed wrapping around the TiO₂ nanoparticles, forming a uniform composite structure. The selected area electron diffraction (SAED) pattern in the lower right corner shows polycrystalline rings, further verifying the polycrystalline nanostructure of TiO₂ [49]. Overall, the TEM and HRTEM results directly reveal the mesoporous nanoporous morphology, anatase crystal phase, and homogeneous composite state of TiO₂ and GO, providing direct microstructural evidence for understanding the enhanced photocatalytic performance of the composite.

Figure 6 presents the transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) characterization results of the TiO₂/GO/CdS mesoporous composite. TEM images (a–d) at different magnifications reveal that the material is composed of densely aggregated nanoparticles with a size of approximately 10–50 nm, retaining abundant mesoporous channels between particles, which aligns with previous BET and SEM results and provides sufficient active sites and mass transfer pathways for photocatalytic reactions. HRTEM images (e–h) display clear lattice fringes corresponding to the (101) crystal plane of anatase TiO₂ and characteristic planes of CdS, respectively, confirming the well-preserved crystallinity of both TiO₂ and CdS. In the HRTEM analysis of the TiO₂/GO binary composite (Figure 5), lattice fringes with a measured d-spacing of 0.35 nm are observed, which match well with the (101) interplanar distance of anatase TiO₂ (0.352 nm, JCPDS No. 21-1272). No other crystalline phases are evident, consistent with the absence of intentional CdS doping. For the TiO₂/GO/CdS ternary composite (Figure 6), multiple sets of lattice fringes can be unambiguously indexed. A d-spacing of 0.351 nm again corresponds to anatase TiO₂ (101). The d-spacings of 0.360 nm and 0.337 nm (and the closely related 0.333 nm) are consistent, respectively, with the (100) and (002) planes of hexagonal CdS (JCPDS No. 41-1049); the value of 0.337 nm may also be assigned to the (111) plane of cubic CdS (JCPDS No. 10-0454). The coexistence of clearly resolved TiO₂ and CdS lattice fringes within the same composite particle directly demonstrates that CdS is successfully incorporated while preserving its own crystallinity, thereby confirming the formation of the intended ternary heterostructure. Meanwhile, thin GO sheets are observed wrapping around the particles, forming a uniform ternary composite structure. The selected area electron diffraction (SAED) pattern shows polycrystalline rings, further verifying the polycrystalline nanostructure of the material [50]. Overall, the TEM and HRTEM results directly reveal the mesoporous nanoporous morphology, crystalline phase composition, and homogeneous composite state of each component in the TiO₂/GO/CdS composite, providing direct microstructural evidence for understanding the enhanced photocatalytic and antibacterial performance.

Figure 7 presents the UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Fourier transform infrared spectroscopy (FT-IR) characterization results of the two composite materials. As shown in Figure 7a, commercial P25 exhibits a sharp drop in absorbance beyond 400 nm, only responding to ultraviolet light; TiO₂/GO shows a slight increase in absorbance in the visible region, while TiO₂/GO/CdS displays significantly enhanced absorbance in the 400–800 nm range with an obvious red-shift in the absorption edge, indicating that the synergistic effect of CdS and GO effectively broadens the visible-light response range and improves the visible-light utilization efficiency of the material [51]. In Figure 7b, both samples show characteristic peaks of hydroxyl groups and adsorbed water at around 3400 cm⁻¹ and 1630 cm⁻¹. Although the overall FTIR spectra of TiO₂/GO and TiO₂/GO/CdS appear broadly similar owing to the dominant absorption bands of GO and the TiO₂ matrix, a detailed high-resolution comparison reveals subtle yet reproducible differences that evidence the chemical interaction among the components. In the region of oxygen-containing functional groups, the C=O stretching vibration of carboxyl groups shifts from ~1725 cm⁻¹ in TiO₂/GO to ~1718 cm⁻¹ in TiO₂/GO/CdS, and the epoxy C–O band at ~1225 cm⁻¹ broadens and shifts to a lower wavenumber (~1220 cm⁻¹). These changes are consistent with the coordination of Cd²⁺ ions to oxygen-containing moieties of GO. Furthermore, a weak shoulder emerges at ~1060 cm⁻¹ in the ternary composite, which can be assigned to Ti–O–C covalent bonds; its enhanced intensity and slight shift relative to that in TiO₂/GO indicate an altered interfacial bonding environment after CdS incorporation. The subtraction spectrum (TiO₂/GO/CdS minus TiO₂/GO) is not a flat baseline but clearly reveals positive residual features at ~650 cm⁻¹ and ~480 cm⁻¹, characteristic of Cd–S stretching modes that are entirely absent in the binary composite. Collectively, these spectroscopic signatures demonstrate that CdS is chemically anchored to the TiO₂/GO framework, confirming intimate interfacial interactions among the three components. Overall, the UV-Vis and FT-IR results demonstrate that TiO₂/GO/CdS possesses superior visible-light response, providing optical and chemical structural evidence for its enhanced photocatalytic and antibacterial performance.

Escherichia coli (ATCC 25922) was selected as a representative Gram-negative model bacterium for this initial evaluation because of its well-characterized response to photocatalytic reactive oxygen species and its widespread use in comparable studies. The evaluation against Gram-positive bacteria will be addressed in future work to fully assess the antibacterial spectrum. Figure 8 presents the visible-light photocatalytic antibacterial performance of the composites against Escherichia coli, which is fully consistent with the previous structural and optical characterizations. As shown in the survival rate histogram (a), the control group (b) and TiO₂/GO group (c) exhibit nearly 100% bacterial survival with only negligible antibacterial effect, while the TiO₂/GO/CdS group (d) shows a sharp decrease in survival rate to approximately 40%, indicating significantly enhanced antibacterial activity. The corresponding colony plate images (b–d) visually confirm this result: dense colonies are observed in the control and TiO₂/GO groups, whereas the number of colonies is drastically reduced in the TiO₂/GO/CdS group, demonstrating its excellent visible-light photocatalytic bactericidal ability. This enhanced performance can be reasonably explained by the earlier characterizations: BET and TEM results reveal that TiO₂/GO/CdS possesses a developed mesoporous structure and high specific surface area, providing sufficient active sites for bacterial adsorption and photocatalytic reactions; UV-Vis DRS spectra confirm that the synergistic effect of CdS and GO effectively broadens the visible-light response range and improves photon utilization efficiency; XPS and HRTEM verify the strong interfacial interaction between components, which efficiently suppresses the recombination of photogenerated carriers and promotes the generation of reactive oxygen species (ROS), leading to efficient inactivation of Escherichia coli. Overall, the structural advantages, optical properties, and antibacterial performance of TiO₂/GO/CdS are highly consistent, fully demonstrating that the CdS composite is an effective strategy to enhance the performance of TiO₂-based photocatalytic antibacterial materials, providing experimental support for its practical application in the antibacterial field. The survival rate of ~40% for E. coli under visible light observed here is lower (better antibacterial effect) than the ~60% survival reported for hierarchical TiO₂/CdS spindle-like composites under similar light conditions [25], likely due to the higher specific surface area and more efficient charge separation in the present mesoporous ternary system.

4. Conclusions

In this study, a TiO₂/GO/CdS mesoporous nanocomposite was successfully prepared via an ultrasound-assisted sol–gel method, and its structure, morphology, and optical properties were systematically characterized, while its visible-light photocatalytic antibacterial performance was evaluated using Escherichia coli as a model strain. The results show that the as-prepared composite retains a well-developed mesoporous structure with a specific surface area of 197.0962 m²/g and a pore size distribution concentrated in 2–14 nm, providing sufficient active sites and mass transfer channels for photocatalytic reactions. XPS, TEM, and XRD results confirm that CdS is successfully incorporated into the TiO₂/GO matrix, with uniform distribution of each component and good interfacial bonding without destroying the anatase crystal phase of TiO₂. UV-Vis DRS reveals that the synergistic effect of CdS and GO significantly broadens the visible-light response range of the material and improves photon utilization efficiency. Antibacterial tests demonstrate that TiO₂/GO/CdS can reduce the survival rate of Escherichia coli to approximately 40% under visible light, exhibiting far superior antibacterial activity compared to pure TiO₂ and TiO₂/GO composite. The relatively moderate antibacterial efficiency (approximately 60% inactivation) of the TiO₂/GO/CdS composite can be attributed to several inherent and experimental factors. First, despite the formation of a heterostructure, residual recombination of photogenerated electron–hole pairs still occurs within the photocatalyst, limiting the yield of reactive oxygen species. Second, the well-developed mesoporous framework, while providing high surface area, may also scatter a fraction of the incident visible light, thereby reducing the effective photon absorption. Third, CdS is known to suffer from photocorrosion, which gradually degrades the active heterojunction interface and releases Cd²⁺ ions, compromising the stability and sustained generation of reactive radicals during the antibacterial test. Fourth, the bactericidal action relies on short-lived reactive oxygen species, such as hydroxyl and superoxide radicals, which can only diffuse over very limited distances; therefore, only bacteria in immediate contact with the catalyst surface are effectively inactivated, while those suspended in the solution may survive. Finally, the experimental conditions—including the relatively low photocatalyst dosage (5 mg in 30 mL), the intensity of the visible light source, and the 4 h exposure time—may not be sufficient to achieve much higher inactivation levels, indicating that the reported value likely does not represent the intrinsic upper limit of the composite. This performance enhancement stems from the synergistic effect of the mesoporous structure, enhanced visible-light response, and suppressed carrier recombination, providing a new strategy for the modification of TiO₂-based photocatalytic antibacterial materials and showing promising application prospects in environmental purification and antibacterial fields.