INTRODUCTION
Research rationale
The current population explosion and increased demand for natural and artificial resources have severely impacted our environment, leading to significant pollution of water, soil, and air This environmental degradation poses one of the greatest challenges of the 21st century, affecting both humans and other living organisms To address this issue, various strategies have been proposed to prevent and mitigate environmental damage while meeting human needs One promising solution is the reuse of water through wastewater treatment in agricultural and industrial sectors.
To address the escalating clean water shortage, the development of cost-effective and efficient wastewater treatment techniques is essential Recently, the photo-degradation process using nanoparticles has gained significant attention from researchers due to its advantages over traditional water treatment methods One notable approach is Heterogeneous Photocatalytic Oxidation (PCO), which effectively reduces low concentrations of organic contaminants in gaseous effluents, converting them into environmentally safe products (Blount, Kim, & Falconer, 2001) Among various photocatalysts, Nano-TiO2 stands out for its high efficiency, affordability, stability, widespread availability, and non-corrosive nature (Carp, Huisman, & Reller, 2004; Dong et al., 2015; Herrmann et al., 2007).
The practical use of TiO2 has been limited due to challenges in separating and recovering it from liquid phases (Dong et al., 2015) To address this issue, various methods have been explored, including the immobilization of TiO2 nanoparticles on different supports While multiple techniques for creating thin films with nanostructured TiO2 exist, they often involve complex processes and costly equipment, which can lead to nanoparticle agglomeration during fabrication (Kim & Sohn, 2002) However, previous studies have highlighted layer-by-layer self-assembly as a promising technique for fabricating thin films containing TiO2 nanoparticles (Dong et al., 2015).
This study focused on the fabrication of various films composed of TiO2 and Poly(L-Dopa) through a layer-by-layer self-assembly technique The films were analyzed using UV-Vis spectroscopy and characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM) These methods were employed to evaluate the films' effectiveness in practical applications, particularly regarding the low-cost and high reusability of TiO2 particle immobilization Additionally, Poly(acrylic acid) (PAA) was utilized to confirm the role of Poly(L-Dopa) in the process.
B (SRB) was used as a model to study the “photocatalytic activity” luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
Research’s objectives
The research aims to prepare TiO2 films with high optical transparency through layer-by-layer self-assembly using commercial TiO 2 and Poly(L-Dopa).
Research questions and hypotheses
The procedure for fabricating [TiO2/Poly(L-Dopa)]n films involves a multilayer assembly technique that utilizes the unique properties of Poly(L-Dopa) (Pdopa) as a binder and stabilizer Pdopa plays a crucial role in enhancing the photocatalytic activity of the films by promoting the uniform distribution of TiO2 nanoparticles and improving their adhesion When comparing the effectiveness of various TiO2 catalysts, P25 Degussa, St-01, and St-21 demonstrate differing efficiencies in the fabrication of these films, with significant variations in their ability to degrade pollutants under light exposure.
Limitations
The research faced time constraints, limiting its scope compared to other experiments.
LITERATURE REVIEW
Overview of Titanium dioxide
2.1.1 Titanium oxidation structures and properties
Titanium dioxide (TiO2), an n-type semiconductor, is extensively used as a photocatalyst for environmental pollutant decomposition due to its high efficiency, low cost, and biological inertness This nano-TiO2 photocatalyst stands out among metal oxides for its physical and chemical stability, widespread availability, noncorrosive nature, and safety for both humans and the environment.
Titanium dioxide (TiO2) exists in three polymorphic forms: anatase, rutile, and brookite Rutile is the most stable and primary source of TiO2, while anatase exhibits superior photocatalytic activity compared to the other phases The band gap of anatase is 3.2 eV, rutile is 3.0 eV, and brookite is approximately 3.2 eV Rutile can be excited by both visible and ultraviolet (UV) light, whereas anatase is only responsive to UV light, and brookite does not respond to UV light.
Titanium (Ti 4+) atoms are coordinated with six oxygen (O 2−) atoms to form TiO6 octahedra across three distinct phases, as illustrated in the accompanying figure, where titanium atoms are depicted in gray and oxygen atoms in red Anatase can undergo a transformation into rutile when subjected to high temperatures, while brookite, characterized by its orthorhombic crystal system, can also convert to rutile through the application of heat.
Figure 1 Crystal structures of rutile, anatase and brookite titanium dioxide
P25, produced by Degussa in Japan, is synthesized from titanium chloride at elevated temperatures and consists of 80% anatase and 20% rutile In contrast, ST-01 and ST-21, manufactured by Ishihara Sangyo Co Ltd., are 100% anatase powders derived from titanium sulfonate (Zarei et al., 2010).
2.1.2 The photocatalytic activity of TiO 2
When nano-TiO2 is exposed to ultraviolet (UV) light, it promotes electrons from the valence band to the conduction band, creating energized holes These free electrons react with oxygen to form superoxide radical anions, while the energized holes interact with water or hydroxyl ions to produce hydroxyl radicals The combination of photogenerated holes and hydroxyl radicals effectively oxidizes and decomposes organic contaminants.
Figure 2 Schematic diagram illustrating the principle of TiO2 photocatalysis with the presence of water pollutant (RH)(Dong et al., 2015)
Despite its potential, the practical applications of TiO2 are hindered by several limitations These include its low absorption capacity for hydrophobic contaminants, a high tendency for particle aggregation, and challenges in the separation and recovery of TiO2 particles from liquid phases (Dong et al., 2015).
Layer-by-layer self-assembly
Layer-by-layer self-assembly (LBL-SA) is a versatile bottom-up method offering superior structure control for fabrication of multilayer films(Zhang, Xu, Sun,
LBL-SA is a promising method that utilizes a straightforward process involving spontaneous ionic adsorption of oppositely charged materials from aqueous solutions This technique allows for the construction of ultrathin layers, approximately 1 nm thick, composed of polymer and inorganic TiO2.
(∼3 nm) molecules by the stepwise construction of molecular-level ordered luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
TiO 2 /polymer nanocomposite films without costly equipment(Kim & Sohn, 2002; Kotov, Dekany, & Fendler, 1995; Y J Liu, Wang, & Claus, 1997; Xiang, Lu, & Jiang,
2012) For photocatalytic coatings, TiO2 nanoparticles with ionic charges on their surface can be effectively incorporated into thin films without severe agglomeration by the LBL-SA method (Kim & Sohn, 2002)
Figure 3 The principle of Layer-by-layer self-assembling method(Kim & Sohn,
2002; Kotov et al., 1995; Y J Liu et al., 1997; Xiang et al., 2012)
The multilayer films were fabricated using positively charged nano-TiO2 particles and negatively charged Poly(L-Dopa) To create the initial negatively charged layer, a Piranha solution was utilized.
Overview of Poly(L-Dopa)
Figure 4.Poly(L-DOPA)(Gu, Fu, Wu, & Zhang, 2016; Yu, Liu, Yuan, Brown, &
3,4-Dihydroxy-L-phenylalanine (L-DOPA) is an essential antiparkinsonian agent and a natural isomer of dopamine's immediate precursor It plays a significant role in mussel adhesive proteins and exhibits strong binding capabilities to various natural and synthetic materials L-DOPA's actions mirror those of dopamine, as dopamine is formed through the decarboxylation of L-DOPA This compound can be deposited on a wide range of inorganic and organic substrates, including super hydrophobic surfaces, allowing for controllable film thickness and durability Additionally, Poly(L-DOPA) is produced through the self-polymerization of L-DOPA, retaining its beneficial properties.
METHODS
Material
Figure 5 Chemicals: a) PDopa, b) SRB 10 uM, c) DIW pH=3, d) PAA
Degussa P25 was utilized as received, while St-01 and St-21 were sourced from Ishihara Sangyo Co Ltd Poly(L-Dopa) was synthesized from L-Dopa (≥ 98%) PAA, SRB (C27H30N2O7S2), and a 30% hydrogen peroxide solution were procured from Sigma-Aldrich, and sulfuric acid (95.0-98.0%) was obtained from J.T.Baken Chemicals Doubly de-ionized water was prepared using a Milli-Q system (Millipore, Bedford, MA, USA) with a resistivity of 18.2 M-cm.
Figure 6 Equipment: a) UV-Visible Spectrophotometer, b) Photochemical reactor, c) pH adjustment, d) Magnetic stirrer, e) Ultrasonic, f) DLS
- Zetasizer Nano ZS instrument (ZEN 3600, Malvern Instruments Ltd.)
- UV-Vis (Varian (Cary-50 Bio)) spectrometer
- Scanning Electron Microscopy (SEM) (a HITACHI SU8010 scanning electron microscopy)
- Atomic Force Microscopy: a Dimension ICON model (Bruker Corp.)
Methods
Multilayer films were fabricated using different types of TiO2, specifically Degussa P25, St-01, and St-21, under consistent conditions The resulting LBL TiO2/Poly(L-Dopa) multilayer films were analyzed using UV-vis spectroscopy and characterized through DLS, SEM, FTIR, and AFM to assess the impact of varying particle sizes and surface zeta-potential of TiO2 Additionally, Poly(acrylic acid) (PAA) was employed to investigate the role of Poly(L-Dopa), while Sulforhodamine B (SRB) served as a model for evaluating photocatalytic activity.
3.2.2 Fabrication of photocatalytic thin [TiO 2 / Polymer] n films by the layer-by- layer self-assembly
After cut into small slides with area of 25x09 mm, Glass substrates were cleaned in a piranha solution (70/30 v/v of concentrated H 2 SO 4 and 30% H 2 O 2 ) in order to generate negatively charged surfaces
Preparation of polymer solution (pH 3.0 , C = 2g/l) luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
For each two-film fabrication, After 36 mg polymer was dissolved in 18 ml DIW, the pH of this solution was adjusted to 3.0 by HNO 3 This solution was sonicated for
Preparation of TiO 2 solution (pH3.0, C = 1g/l)
Before sonication TiO 2 solution for 10 minutes, 18 mg TiO 2 was measured and dispersed in 18 ml DIW, and then adjusted until pH=3.0 by HNO 3
PH adjustments TiO 2 solution and polymer solution were adjusted by Portable pH meter
Firstly, using base [pH4] and [pH7] to create baseline
- Click [Cal] button and then [v] until “Different electrode for pH” occurs in the screen
- After washed, pH meter was dipped into [pH4] to create baseline, and then click [v]
- pH meter was washed again and then dipped into [pH7]
- TiO 2 solution and polymer solution with stir bar inside were put in Magnetic stirrer
[TiO 2 / Polymer] n film procedures luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
To fabricate multilayer thin films of TiO2/polymer, each film was immobilized in a petri dish using clips, tongs, and magnets Two glass slides were sequentially dipped into a solution for five minutes and then washed with deionized water adjusted to pH 3.0 using HNO3 This controlled dipping sequence allowed for the creation of Layer-by-Layer Self-Assembled (LBL-SA) thin films with a specified number of layers, as detailed in the accompanying table The entire experiment was conducted at room temperature, with TiO2 solutions utilized for both the initial and final dips.
Films Numbers of TiO 2 layers Numbers of Polymer layer
Finally, the films were dried in oven at 55 o C
P25, St-01, and St-21 solutions were prepared with a pH of 3 and a concentration of 1 g/l to assess particle size and zeta potential.
Poly(L-Dopa) solutions and P25 solutions (1g/l concentration) with different pH from 1 to 5 were prepared in order to measure the variety of zeta-potential with different pH
Dynamic light scattering (DLS) measurements were conducted using a Zetasizer Nano ZS instrument (ZEN 3600, Malvern Instruments Ltd.) to determine the hydrodynamic size and zeta potential of TiO2 suspension and Poly(L-Dopa) The DLS analysis utilized a He-Ne laser with a wavelength of 633 nm and a detection angle of 173°, ensuring precise measurements Additionally, a scanning electron microscopy (SEM) procedure was employed for further analysis.
The multilayer P25/Poly(L-Dopa) thin films' thickness and surface morphology were analyzed using a HITACHI SU8010 scanning electron microscope at 5 kV Unlike the films employed in photodegradation tests, the cores of the SEM-analyzed films are composed of quartz Additionally, Atomic Force Microscopy (AFM) was utilized for further characterization.
AFM scans of 1 μm × 1 μm were conducted using a Dimension ICON model (Bruker Corp.) in tapping-mode at a scan rate of 0.5 Hz with a silicon nitride tip, controlled by Nano-scope software The study measured the root mean squared (RMS) roughness and surface area of the films, alongside Fourier Transform Infrared Spectroscopy (FTIR) analysis.
The dried samples, including Degauss P25, L-Dopa, Poly(L-Dopa), PAA, P25/PAA, and P25/Poly(L-Dopa), were ground with KBr powder (FT-IR grade, Aldrich) prior to measurement The FTIR spectra were obtained using a Nicolet 6700 FT-IR spectrophotometer from Thermo Electron Scientific Instruments Corp.
The UV-Vis spectra of multilayer films on glass slides were analyzed using a Varian Cary-50 Bio spectrometer, focusing on the effects of varying the number of TiO2 layers and the concentration of the SRB solution during the photodegradation process.
The [TiO2/polymer]n films were immersed in a quartz tube containing 2.5 ml of 10 µM SRB solution along with a stir bar, and subsequently placed in a photochemical reactor At intervals of 0, 10, 20, 30, 40, 50, and 60 minutes, the solutions were analyzed using a UV-Visible spectrophotometer to collect data.
-Films absorbance: the films with quartz core were used to test in UV-Vis Spectrophotometer
The calibration of SRB was conducted by measuring the absorbance at concentrations of 0.5, 1, 2, 5, 10, 15, and 20 µM using a Varian Cary-50 Bio UV-Vis spectrometer.
RESULT
Optical Photo
4.1.1 Optical photos of P25/PDopa films
Figure 8 Photos of P25/PDopa film 4.1.2 Optical photos of multiple films a) b) c)
Figure 9 5.5 bilayer thin films' images: a) St-01, b) St-21, c) P25 luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
Characterization of P25/Pdopa
Z et a-p ot en tia l (mV)
Figure 10 TiO 2 size and zeta-potential at (pH=3, concentration = 1g/l)
At pH 3, P25 exhibits the highest zeta potential exceeding 45 mV and the smallest particle size compared to TiO2 St-01 and St-21, resulting in improved stability and a lower sedimentation rate In contrast, the zeta potentials of the other TiO2 variants remain below 40 mV.
269 nm, whereas those of St-01 and St-21 are larger than 390nm luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
Z e ta -p o te n tia l (mV) pH
Figure 11.PDopa zeta-potential and P25 zeta-potential varied from pH
A comparison of the zeta-potential values for P25 and PDopa across pH levels 1 to 5 reveals that both exhibit optimal stability at pH 3 Specifically, P25 shows a decrease in zeta-potential from 49 mV to 40 mV, while PDopa demonstrates significantly low values at pH 1 and 2, indicating strong aggregation in the liquid phase Notably, the zeta-potential values for both materials improve from pH 3 onwards.
5 At pH 4,5Pdopa has good stability, however, the stability of P25 decreases
Figure 12 P25 size varied from pH luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
At pH 3, the particle size of P25 is approximately 200 nm, which helps prevent sedimentation, while at pH 1, the particle size increases to 839 nm The large standard deviation of particle size at pH 1 indicates instability under acidic conditions.
Figure 13 FT-IR spectra of Degussa P25, L-Dopa, PDopa, P25/PDopa, PAA,
The multilayer thin films retain the essential functional groups of the original chemicals, as evidenced by FTIR peak comparisons between P25/Pdopa and bare P25, Pdopa, as well as P25/PAA and bare P25, PAA Notable shifts in the vibration peaks of C=H and N-H groups indicate coordination between carboxylic groups and Ti atoms The FTIR analysis reveals that the structural integrity and characteristics of P25 and PDopa remain intact following the fabrication of multilayer films through the layer-by-layer self-assembly method.
4.2.3 SEM images of P25/Pdopa a) b) c) luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si d) e) f) luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si g)
Figure 14 SEM images of (a) 0.5 bilayers, (b) 1.5 bilayers, (c) 2.5 bilayers, (d) 5.5 bilayers, (e) 10.5 bilayers, (f) 15.5 bilayers, (g) 20.5 bilayers
The layer-by-layer self-assembling method significantly enhanced the thickness of TiO2 films, as illustrated in Figure 14 Initially, with 0.5 layers (1 layer of P25), the film thickness varied between 31.7 nm and 73.4 nm After applying 5.5 bilayers of P25/PDopa, the thickness increased to approximately 83.3 nm to 288 nm Notably, the film with 20 bilayers exhibited an even greater thickness and homogeneity, measuring around 438 nm.
4.2.4 AFM a) luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si b) c) d) e) f) luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si g) h)
AFM images illustrate the thin films created using the coating sequence of (P25/PDopa) n, showcasing various bilayer counts: a) 0.5 bilayers, b) 2.5 bilayers, c) 5.5 bilayers prior to UV photodegradation, d) 5.5 bilayers post-UV photodegradation, e) 5.5 bilayers after further photodegradation, f) 10.5 bilayers, g) 15.5 bilayers, and h) 20.5 bilayers.
The formation and morphological changes of multilayer thin films composed of P25 and Pdopa are influenced by the number of bilayers, resulting in increased density with more deposition rounds AFM images reveal rough surfaces, showcasing visible TiO2 clusters, indicating that the growth process does not occur in a perfect layer-by-layer manner Instead, TiO2 nanoparticles fill the pores and accumulate, contributing to simultaneous thickness growth.
A comparison of 5.5 bilayers before and after photodegradation reveals the presence of TiO2 particles in the films, highlighting the potential for reusability of the multilayer films.
Table 2 Roughness of P25/PDopa films with different numbers of bilayer
The roughness of the films was not influenced by the number of TiO2 and PDopa bilayers; the maximum roughness was observed in 5.5 bilayers, while the minimum occurred in 10.5 bilayers.
Photodegradation performance
Ab so rb an ce
Figure 16 Absorbance of SRB: a) in range from 400nm to 750nm, b) at 562nm
The calibration data set presented shows a linear relationship between concentration (X) and absorbance at 562 nm (Y = 0.0928x - 0.005), with black dots representing the data points The measured slope is 0.928, and the intercept is 0.005 Notably, the true slope value, including the blank, is 7, indicating a strong quality of fit.
(standard deviation) is 0.9999, which shows high quality of this method in concentration range from 0.5 uM to 20 uM
4.3.2 Photodegradation activities of PDopa films
2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers a)
5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers ln (C /C 0 )
The photodegradation profiles of (P25/PAA)nthin films for the dye SRB were analyzed at a wavelength of 562 nm, revealing significant degradation efficiency The first-order kinetic analysis, represented by the plot of ln(C/C0) against time in minutes, demonstrates the effectiveness of (P25/PAA)n thin films in facilitating the photodegradation process of SRB at the specified wavelength.
The efficiencies of photocatalytic degradation under UV-vis irradiation are illustrated in Figure 17(a), where C represents the concentration of SRB at time t and C0 denotes the concentration of photocatalysts in absorption equilibrium prior to irradiation The data indicates that P25/PAA bilayer films exhibit significant photocatalytic activity, with approximately 98% degradation of SRB solutions after 1 hour for 20.5 bilayers, compared to 85% for 2.5 bilayers films produced through dip-coating This enhancement in photocatalytic efficiency is attributed to the layer-by-layer structure Furthermore, Figure 17(b) presents the correlation between time and ln(C/C0) for all photocatalysts, highlighting that the photocatalytic efficiency of the 20.5 bilayer P25/PAA composite is twice that of the 2.5 bilayer film.
2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers
2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayers ln (C /C 0 )
Figure 18 (a) SRB degradation profiles of (P25/PDopa)n thin films at wavelength
The photodegradation of SRB using (P25/PDopa)n thin films was analyzed at a wavelength of 562 nm The first-order kinetic plot, which illustrates the relationship between the natural logarithm of the concentration ratio (C/C0) and time in minutes, demonstrates the effectiveness of the thin films in this process For further insights and detailed findings, the thesis can be downloaded from the provided email address.
Multilayer films incorporating Poly(L-Dopa) demonstrated significantly higher photodegradation efficiency, achieving nearly 99% degradation of SRB solutions after just 1 hour of irradiation with 20.5 bilayer films In contrast, films made by dip-coating with only 2.5 bilayers resulted in a degradation rate of 89%.
The degradation profiles of SRB in (TiO2/PDopa)n thin films were analyzed at a wavelength of 562 nm, revealing the effectiveness of different TiO2 types in photodegradation Additionally, the first-order kinetic plot of ln(C/C0) versus time (in minutes) demonstrates the relationship between concentration changes and time during the photodegradation process.
The degradation profiles of SRB in multilayer films with various types of TiO2 were analyzed, revealing significant differences in photodegradation efficiency The first-order kinetic plot of ln(C/C0) versus time (in minutes) demonstrated that multilayer films containing P25 exhibited a photodegradation efficiency three times greater than that of St-21 and six times greater than St-01.
P25/PDoPa films band gap
2.5 Bilayers 5.5 Bilayers 10.5 Bilayers 15.5 Bilayers 20.5 Bilayer a)
Ab so rb an ce a t 3 00 n m
Figure 20 (a) Absorbance of P25/PDoPa films, (b) Absorbance at 300 nm of
P25/PDoPa, (c) band gap of P25/PDopa luan van tot nghiep download luanvanfull moi nhat z z @gmail.com Luan van thac si
The P25/Pdopa bilayer films exhibit no visible light absorption, with an absorption edge at 400 nm, as illustrated in figure 20(a) Additionally, figure 20(b) demonstrates that the absorbance of the films increases with the number of bilayers at a wavelength of 300 nm.
The band gap of the photocatalyst can be determined using the Kubelka-Munk equation: αhυ = const(hυ − Eg)², where α is defined as (1 − R)² / 2R, with R representing reflectance and A denoting optical absorption As illustrated in Figure 20(c), the plot of (αhυ)¹/² against photon energy reveals that the band gap of P25/PDoPa films is approximately 3.2 eV.
DISCUSSION AND CONCLUSION
Discussion
Photocatalytic thin films created through the layer-by-layer self-assembly method using P25 and poly(L-Dopa) show significant potential for enhancing contaminant degradation efficiency This approach leverages the beneficial properties of both the materials and the fabrication technique, making it a promising solution for improving photodegradation outcomes.
At pH 3, P25 exhibits the highest zeta-potential and the smallest particle size compared to St-01 and St-21, leading to superior colloidal stability and a low sedimentation rate This enhanced stability contributes to the significantly higher photodegradation efficiency of multilayer films containing P25, making it an ideal choice for fabrication at this pH level.
Poly(L-Dopa) exhibits a negative charge across a wide pH range of 3 to 5, with a Zeta-potential of less than -30 mV, while P25 demonstrates a strong positive charge from pH 1 to 5, with a Zeta-potential exceeding 40 mV and a smaller particle size between pH 2 and 4 According to Anirbandeep Bose's research on Zeta potential and nanoparticle stability, a Zeta-potential range of ±30 to ±60 indicates moderate to good stability of colloids Therefore, solutions of P25 and Poly(L-Dopa) at pH levels between 3 and 5 are considered optimal for stability.
Multilayer films incorporating Poly(L-Dopa) demonstrate superior photodegradation efficiency compared to those made with PAA This finding supports previous research advocating for the use of Poly(L-Dopa) in the production of multilayer films.
The FTIR analysis reveals that the multilayer films retain the functional groups and properties of both bare P25 and PDopa, as evidenced by the similar peaks observed in the spectra This indicates that the multilayer films share the same functional groups as their constituent materials.
SEM and AFM images reveal that the multilayer films' thickness increases with the addition of both P25 and PDopa layers, demonstrating the effectiveness of the layer-by-layer self-assembly method However, the growth of film thickness does not occur in a perfect one-layer-at-a-time manner, as TiO2 nanoparticles also fill the pores and contribute to simultaneous thickness growth.
The photodegradation performance of P25 and PDopa demonstrates their effectiveness when combined, with an increase in bilayers leading to a higher photodegradation rate The multilayer films exhibit a band gap of 3.2 and show limited visible light absorption, similar to the band gap of bare P25, as noted in previous studies (Amtout & Leonelli, 1995; Asahi et al., 2000; Koelsch et al., 2004; Pelaez et al., 2012).
The study reveals limitations, notably that it only examined a maximum of 20.5 bilayers, raising questions about the feasible maximum for optimal fabrication Additionally, the research focused solely on the photodegradation performance of multilayer films in SRB, making it difficult to definitively assert that P25/PDopa is effective in pollution degradation Future research could explore these aspects further for more comprehensive insights.
Conclusion
This study highlights the significance of particle size and colloidal stability in TiO2 aqueous suspensions for enhancing photocatalytic performance Poly(L-Dopa) demonstrates negative charge across a broad pH range, making it a viable alternative to commercially available polyelectrolytes At pH 3, the combination of P25 Degussa and Poly(L-Dopa) exhibits optimal charge, high zeta potential, and reduced particle size, which together ensure excellent colloidal stability and minimal sedimentation Additionally, the layer-by-layer self-assembly technique proves to be a cost-effective and efficient method for creating nano-structured thin films of P25 nanoparticles and Poly(L-Dopa), leveraging the 3.2 eV band gap of bare P25 and the functional properties of Poly(L-Dopa) for effective contaminant decomposition The optimal bilayer configuration identified in this research is 20.5 layers of P25 and Poly(L-Dopa).
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