Surface modification of TiO2 with polydopamine and its effect on photocatalytic degradation mechanism

Synthesis, spectroscopy, band gap energy and electrical conductivity of poly(dopamine-co-aniline) copolymer

Copolymerization is used to improve the solubility and processability of polymers and copolymers includes the individual properties of homopolymer. In this study, the poly(dopamine-co-aniline) (poly(DA-co-ANI) copolymer was synthesized and the UV-vis. absorption, optical band gap energy, fluorescence, FT-IR, SEM-EDS, MALDI-TOF-MS, XRD and electrical conductivity have been investigated. The obtained results for the poly(DA-co-ANI) copolymer were compared with the PDA and PANI homopolymers. It was observed that the poly(DA-co-ANI copolymer is soluble easily in NMP and DMF solvents. The optical band gap energy of the poly(DA-co-ANI) copolymer film were calculated. as 1.00 eV with favorable indirect transition. The poly(DA-co-ANI) copolymer showed the FL emission maximum bands at 390 and 533 nm wavelengths. It was observed from the SEM images that the poly(DA-co-ANI) has 0-1500 nm crystalline rectangular particles prepared in acidic media and 0-600 nm amorphous particles prepared in basic media. The electrical conductivity of the poly(DA-co-ANI) was 1.35 × 10-6 S/cm. In the MALDI-TOF-MS measurements, the number-average molecular weight of the copolymer was found as 2628 Da with a distribution up to 5500 Da. The poly(DA-co-ANI) copolymer, soluble in NMP and DMF solvents and with a low optical band gap energy can be utilized as optical, fluorescent, and semi-conductive material in biomedical applications.

Catalytic degradation of rhodamine B by titanium dioxide doped polydopamine photoresponsive composites

Titanium dioxide-based materials treat wastewater contaminated by organic pollutants. However, the wide band gap and the ease of agglomeration limit its photocatalytic activity. PDA/PEI@TiO2@P-HSM composites were synthesized using PDA/PEI as an interfacial bonding modifier via polymerization reaction. Phase and chemical bonding analysis confirmed the modifiedTiO2 coated P-HSM, which can effectively reduce the band gap and control the agglomeration of titanium dioxide, i.e., suitable to degrade RhB. Under UV irradiation, PDA/PEI @TiO2@P-HSM can remove RhB up to 90 % in 100 min. The photocatalytic degradation process conforms to the Langmuir-Hinshelwood quasi-primary equation. The composite exhibited excellent stability and recycling i.e., a high removal effect, with a removal rate of up to 60 % after seven cycles of reaction.

Emerald eco-synthesis: harnessing oleander for green silver nanoparticle production and advancing photocatalytic MB degradation with TiO2&CuO nanocomposite

The tertiary composite of TiO2/CuO @ Ag (TCA) were synthesized by the solid state method using different ratios of TiO2/CuO NCs and Ag NPs. The structural, morphological, and optical properties of nanocomposites were analyzed by scanning electron microscope, Transmission electron microscope, X-ray diffraction, Fourier transform infrared spectra, UV-Vis diffuse reflectance spectra (UV-Vis/DRS) and photoluminescence spectrophotometry. The results showed enhanced activity of TCA hybrid nano crystals in oxidizing MB in water under visible light irradiation compared to pure TiO2. The photocatalytic performance TCA samples increased with suitable Ag content. The results show that the photo degradation efficiency of the TiO2 compound improved from 13 to 85% in the presence of TiO2-CuO and to 98.87% in the presence of Ag containing TiO2-CuO, which is 7.6 times higher than that of TiO2. Optical characterization results show enhanced nanocomposite absorption in the visible region with long lifetimes between e/h+ at optimal TiO2-CuO/Ag (TCA2) ratio. Reusable experiments indicated that the prepared TCA NC photo catalysts were stable during MB photo degradation and had practical applications for environmental remediation.

Laser-Induced Graphitization of Polydopamine on Titania Nanotubes

Since the discovery of laser-induced graphite/graphene, there has been a notable surge of scientific interest in advancing diverse methodologies for their synthesis and applications. This study focuses on the utilization of a pulsed Nd:YAG laser to achieve graphitization of polydopamine (PDA) deposited on the surface of titania nanotubes. The partial graphitization is corroborated through Raman and XPS spectroscopies and supported by water contact angle, nanomechanical, and electrochemical measurements. Reactive molecular dynamics simulations confirm the possibility of graphitization in the nanosecond time scale with the evolution of NH3, H2O, and CO2 gases. A thorough exploration of the lasing parameter space (wavelength, pulse energy, and number of pulses) was conducted with the aim of improving either electrochemical activity or photocurrent generation. Whereas the 532 nm laser pulses interacted mostly with the PDA coating, the 365 nm pulses were absorbed by both PDA and the substrate nanotubes, leading to a higher graphitization degree. The majority of the photocurrent and quantum efficiency enhancement is observed in the visible light between 400 and 550 nm. The proposed composite is applied as a photoelectrochemical (PEC) sensor of serotonin in nanomolar concentrations. Because of the suppressed recombination and facilitated charge transfer caused by the laser graphitization, the proposed composite exhibits significantly enhanced PEC performance. In the sensing application, it showed superior sensitivity and a limit of detection competitive with nonprecious metal materials.

Photocatalytic and Photothermal Antimicrobial Mussel-Inspired Nanocomposites for Biomedical Applications

Bacterial infection has traditionally been treated with antibiotics, but their overuse is leading to the development of antibiotic resistance. This may be mitigated by alternative approaches to prevent or treat bacterial infections without utilization of antibiotics. Among the alternatives is the use of photo-responsive antimicrobial nanoparticles and/or nanocomposites, which present unique properties activated by light. In this study, we explored the combined use of titanium oxide and polydopamine to create nanoparticles with photocatalytic and photothermal antibacterial properties triggered by visible or near-infrared light. Furthermore, as a proof-of-concept, these photo-responsive nanoparticles were combined with mussel-inspired catechol-modified hyaluronic acid hydrogels to form novel light-driven antibacterial nanocomposites. The materials were challenged with models of Gram-negative and Gram-positive bacteria. For visible light, the average percentage killed (PK) was 94.6 for E. coli and 92.3 for S. aureus. For near-infrared light, PK for E. coli reported 52.8 and 99.2 for S. aureus. These results confirm the exciting potential of these nanocomposites to prevent the development of antibiotic resistance and also to open the door for further studies to optimize their composition in order to increase their bactericidal efficacy for biomedical applications.

Visible-Light-Driven Photocatalytic Dehydrogenation of Alcohols on TiO2 via Ligand-to-Metal Charge Transfer for Coproduction of H2 and Aldehydes

Developing visible-light-driven photocatalysts for the catalytic dehydrogenation of organics is of great significance for sustainable solar energy utilization. Here, we first report that aromatic alcohols could be efficiently split into H₂ and aldehydes over TiO₂ under visible-light irradiation through a ligand-to-metal charge transfer (LMCT) mechanism. A series of TiO₂ catalysts with different surface contents of the hydroxyl group (-OH) have been synthesized by controlling the hydrothermal and calcination synthesis methods. An optimal H₂ production rate of 18.6 μmol h^-1 is obtained on TiO₂ synthesized from the hydrothermal method with a high content of surface -OH. Experimental characterizations and comparison studies reveal that the surface -OH markedly influences the formation of LMCT complexes and thus changes the visible-light-driven photocatalytic performance. This work is anticipated to inspire further research endeavors in the design and fabrication of visible-light-driven photocatalyst systems based on the LMCT mechanism to realize the simultaneous synthesis of clean fuel and fine chemicals.

Shaddock peel-derived N-doped carbon quantum dots coupled with ultrathin BiOBr square nanosheets with boosted visible light response for high-efficiency photodegradation of RhB

In the present work, we constructed a serials of novel shaddock peel-derived N-doped carbon quantum dots (NCQDs) coupled with BiOBr composites. The result showed that the as-synthesized BiOBr (BOB) was composed of ultrathin square nanosheets and flower-like structure, and NCQDs were uniformly dispersed on the surface of BiOBr. Furthermore, the BOB@NCQDs-5 with optimal NCQDs content displayed the top-flight photodegradation efficiency with ca. 99% of removal rate within 20 min under visible light and possessed excellent recyclability and photostability after 5 cycles. The reason was attributed to relatively large BET surface area, the narrow energy gap, inhibited recombination of charge carriers and excellent photoelectrochemical performances. Meanwhile, the improved photodegradation mechanism and possible reaction pathways were also elucidated in detail. On this basis, the study opens a novel perspective to obtain a highly efficient photocatalyst for practical environment remediation.

Kinetic study of polydopamine sphere synthesis using TRIS: relationship between synthesis conditions and final properties

The synthesis and characterization of polydopamine (PDA) using dopamine (DA) as the monomer and (hydroxymethyl)aminomethane (TRIS) as the oxidant is studied. The effect of temperature and TRIS concentration on the kinetics of dopamine polymerization is evaluated, and the kinetic parameters are also calculated. Three TRIS concentrations are used to assess their effect on DA polymerization kinetics. The reaction at 1.5 mmol of TRIS shows a sustained increase of the rate constant with temperature from 2.38 × 10^-4 to 5.10 × 10^-4 when the temperature is increased from 25 to 55 °C; however, not all reactions follow an Arrhenius law. In addition, the correlation between the synthesis parameters and morphological, structural, and thermal properties of polydopamine is established. The morphology of the PDA particles is evaluated by Scanning Electron Microscopy (SEM), the relationships between the diameter, distribution size, and the rate constant. Thermal characterization by Differential Scanning Calorimetry (DSC) shows an endothermic transition around 130 °C associated with the melting of PDA's regular structure. It is supported by structural studies, such as infrared and Raman spectroscopy and X-ray Diffraction (XRD), by observing a broad peak at 23.1° (2θ) that fits with a graphitic-like structure of PDA.

Photocatalytic mechanism conversion of titanium dioxide induced via surface interface coordination

Photocatalytic removal of organic pollutants is a promising pollution treatment technology from the aspect of carbon neutrality. The complex diversity of actual wastewater components, as opposed to single-component systems, can significantly affect photocatalytic mechanisms. In this study, complex pollutant systems were created using various coordinating agents, and the effects of P25 on the photocatalytic removal of methyl orange (MO) in these systems and corresponding photocatalytic mechanism were investigated. The results show that photocatalytic removal of MO by P25 using ligands is significantly more efficient, especial removal of MO by the EDTA-P25 (P-E_2.5) coordination system resulted dramatically improved MO removal (97.4% versus 12.3% achieved by pure P25 after 15 min), with the reaction rate improved 23.8-fold. Theoretical calculations show that the effective coordination bonds formed by the coordinating agent and Ti atoms reduce the adsorption energy of P25 for MO. In addition, introduction of the coordinating agent EDTA reduces the transition state energy during the MO degradation process and greatly accelerates the reaction rate, and the conduction band position of the EDTA-P25 coordination system shifts to a more negative potential, which induces to the generation of •O₂^- for effective MO degradation.

Property-governed performance of platinum-modified titania photocatalysts

Titania is probably the most widely investigated semiconductor photocatalyst because of various advantages, such as high activity, thermal and chemical stability, low price, abundance, and negligible toxicity. However, pristine titania is also characterized by charge carriers’ recombination, and thus lower quantum yields of photocatalytic reactions than theoretical 100%. Moreover, its wide bandgap, despite being recommended for excellent redox properties, means also inactivity under visible part of solar radiation. Accordingly, titania has been surface modified, doped and coupled with various elements/compounds. For example, platinum deposited on the surface of titania has shown to improve both UV activity and the performance under vis. Although the studies on titania modification with platinum started almost half a century ago, and huge number of papers have been published up to now, it is unclear which properties are the most crucial and recommended to obtain highly efficient photocatalyst. In the literature, the opposite findings could be found on the property-governed activities that could result from huge differences in the reaction systems, and also examined photocatalysts. Considering the platinum properties, its content, the size of nanoparticles and the oxidation state, must be examined. Obviously, the characteristics of titania also influence the resultant properties of deposited platinum, and thus the overall photocatalytic performance. Although so many reports on Pt/TiO₂ have been published, it is hardly possible to give indispensable advice on the recommended properties. However, it might be concluded that usually fine platinum NPs uniformly deposited on the titania surface result in high photocatalytic activity, and thus in the low optimal content of necessary platinum. Moreover, the aggregation of titania particles might also help in the lowering the necessary platinum amount (even to 0.2 wt%) due to the interparticle electron transfer mechanism between titania particles in one aggregate. In respect of platinum state, it is thought that it is highly substrate-specific case, and thus either positively charged or zero valent platinum is the most recommended. It might be concluded that despite huge number of papers published on platinum-modified titania, there is still a lack of comprehensive study showing the direct correlation between only one property and the resultant photocatalytic activity.

Polydopamine-Bi2WO6-Decorated Gauzes as Dual-Functional Membranes for Solar Steam Generation and Photocatalytic Degradation Applications

The dual-functional Bi2WO6/polydopamine (PDA)-modified gauze membrane has been developed for applications in photocatalytic degradation and solar steam generation. Two types of membrane were prepared by changing the growth sequence of Bi2WO6 nanomaterials and PDA on gauze substrates. The spatial distribution of Bi2WO6 and polydopamine has a great influence on light absorption, photocatalytic degradation, and solar steam generation performances. Bi2WO6 photocatalysts can absorb short-wavelength light for the photocatalytic decoloration of organic dyes. The photothermal polydopamine can convert light into heat for water evaporation. Besides, the gauze substrate provides water transport channels to facilitate water evaporation. The morphology, surface chemistry, and optical properties of Bi2WO6-PDA modified gauzes were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance spectra. The photothermal properties, wetting properties, and solar steam generation rates of the composite films were also studied. Degradation of 96% of indigo carmine was achieved after being irradiated for 120 min in the presence of G/PDA/BWNP. The water evaporation rates of the G/BWP/PDA sample under the irradiation of an Xe lamp (light intensity = 1000 W/m2) reached 1.94 kg·m-2·h-1.

Polydopamine Functionalized Graphene Oxide as Membrane Nanofiller: Spectral and Structural Studies

High-degree functionalization of graphene oxide (GO) nanoparticles (NPs) using polydopamine (PDA) was conducted to produce polydopamine functionalized graphene oxide nanoparticles (GO-PDA NPs). Aiming to explore their potential use as nanofiller in membrane separation processes, the spectral and structural properties of GO-PDA NPs were comprehensively analyzed. GO NPs were first prepared by the oxidation of graphite via a modified Hummers method. The obtained GO NPs were then functionalized with PDA using a GO:PDA ratio of 1:2 to obtain highly aminated GO NPs. The structural change was evaluated using XRD, FTIR-UATR, Raman spectroscopy, SEM and TEM. Several bands have emerged in the FTIR spectra of GO-PDA attributed to the amine groups of PDA confirming the high functionalization degree of GO NPs. Raman spectra and XRD patterns showed different crystalline structures and defects and higher interlayer spacing of GO-PDA. The change in elemental compositions was confirmed by XPS and CHNSO elemental analysis and showed an emerging N 1s core-level in the GO-PDA survey spectra corresponding to the amine groups of PDA. GO-PDA NPs showed better dispersibility in polar and nonpolar solvents expanding their potential utilization for different purposes. Furthermore, GO and GO-PDA-coated membranes were prepared via pressure-assisted self-assembly technique (PAS) using low concentrations of NPs (1 wt. %). Contact angle measurements showed excellent hydrophilic properties of GO-PDA with an average contact angle of (27.8°).

Facilely synthesized cobalt doped hydroxyapatite as hydroxyl promoted peroxymonosulfate activator for degradation of Rhodamine B

Hydroxyapatite (HAP) is a promising supporter of catalyst due to its potential in immobilizing metals stably. HAP supported cobalt-based catalyst (Co-HAP) was synthesized via a facile ion exchange-calcination method to reduce the Co leaching. The synthesized Co-HAP was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS). Cobalt ions were incorporated into HAP structure and Co₃O₄ on HAP surface. Co-HAP showed satisfactory performance in peroxymonosulfate (PMS) activation for eliminating Rhodamine B (RhB) in aqueous solution. Co-HAP even revealed a better activity than that of CoFe₂O₄. •OH, SO₄^•- and ¹O₂ were all involved in RhB degradation and ¹O₂ played a leading role. High content of surface oxygen groups could be found on Co-HAP after RhB degradation, which might be resulted from the high amounts of hydroxyl groups. The presence of hydroxyl groups performed the co-catalytic activity of PMS activation in Co-HAP/PMS system.

Bio-inspired construction of melanin-like polydopamine-coated CeO2 as a high-performance visible-light-driven photocatalyst for hydrogen production

In recent years, cerium oxide has been the most widely studied photocatalyst due to its unique properties.

Comparison of the Phase Transition and Degradation of Methylene Blue of TiO2, TiO2/Montmorillonite Mixture and TiO2/Montmorillonite Composite

Nano-TiO₂ (T), TiO₂/montmorillonite mixture (Mix), and TiO₂/montmorillonite composite (Com) were prepared by using TiOSO₄•2H₂O as the precursor of TiO₂ and montmorillonite as the matrix. The phase transition process of TiO₂ and the degradation of methylene blue (MB) in T, Mix, and Com were studied by x-ray diffraction (XRD), infrared spectrum (IR), scanning electron microscopy with energy spectrum (SEM-EDS), and other methods. The results show that, except for the fact that the heating temperature has a great influence on the phase transition and grain growth of TiO₂, the introduction of montmorillonite has an obvious inhibition effect on the phase transition and grain growth of TiO₂, and the inhibition effect of the Com is obviously stronger than Mix. In Com, Ti–O–Si chemical bond was formed between TiO₂ and oxygen atoms with negative charge on the bottom of the structure layer of montmorillonite, which is the main reason for inhibition effect. However, in Mix, TiO₂ only covers the surface of montmorillonite without breaking the degree of order of montmorillonite and forming no chemical bond with montmorillonite, so the inhibition effect is small. From degradation of MB, it was found that before the structure of montmorillonite was destroyed (400–600°C), the total degradation percentage in Mix (85.3–99.5%) was higher than T and Com. At high temperature (above 700°C), because of the inhibition effect, the total degradation percentage of MB in Com is much larger than T and Mix, even above 1,100°C, the total degradation percentage can still reach at 47%. Therefore, in industrial applications, Mix and Com can be selected to degradation MB, according to the actual application temperature range.