Separation‐Free Polyaniline/TiO2 3D Hydrogel with High Photocatalytic Activity

Inside- and Outside-Coated PANI and/or PIN-TiO2 Nanotubes for Enhanced Photocatalytic Degradation of 4-Nitrophenol in Wastewater

We present a novel approach for enhancing photocatalytic efficiency by developing polyaniline (PANI) and polyindole (PIN)-coated TiO2 nanotubes (TNT) through a combination of chemical oxidation and hydrothermal processes. The PANI-PIN coating was systematically applied to both the internal and external surfaces of the nanotubes to enhance the photocatalytic active sites and optimize pollutant adsorption. The dual-coated structure enhances the interaction with pollutants, facilitating a more efficient degradation of 4-nitrophenol (4-NP) when exposed to visible light. Thorough characterization through X-ray diffraction (XRD), Fourier-transform infrared (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), N2-physisorption, transient photocurrent, diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) validated the exceptional structural and optical properties of the composite. The PANI/PIN polymer coating effectively inhibited electron-hole recombination, leading to a notable enhancement in photocatalytic performance. Among the tested composites, the formulation consisting of 75% PANI and 25% PIN demonstrated remarkable performance, achieving a degradation rate of 99.46% for 4-NP in only 120 min of exposure to visible light. The impressive efficiency stems from its extensive surface area (255.3 m2/g), efficient charge separation, minimized band gap (2.77 eV), and improved light absorption. Moreover, the composite demonstrated remarkable recyclability, preserving its catalytic activity across five cycles without any decline in performance. These results demonstrate the strong potential of 75%PPTN as a promising photocatalyst for environmental remediation.

Optimization of TiO2-natural hydrogels for paracetamol and ibuprofen degradation in wastewaters

Agarose/micrometer titanium dioxide (TiO2) beads were essayed to test the photocatalytic capacity of two of the most widely prescribed drugs worldwide: paracetamol and ibuprofen. Although the initial tests demonstrated promising degradation rates for both drugs, the presence of turbidity, due to TiO2 leakage, during the photocatalytic essays induced to improve the stability of the photocatalytic composites. Among the different strategies adopted to strengthen such materials, crosslinking with citric acid and the use of alternative gelling agents: gellan, agargel™, and agar were chosen. Composites obtained by merging both strategies were characterized and employed to degrade both drugs under a simulated light that mimics the solar spectrum (indoor). Considering the superior degradation rates obtained when agar and agarose were used to shape the titanium oxide particles (up to 70-75% of drug destruction), such composites were subjected to a more realistic experiment (outdoor): solar illumination, tap water, and higher volumes, that should facilitate its ulterior scale up as a real wastewater depollution procedure. Degradation rates between 80 and 90% are attained under such conditions for both drugs.

The enhanced photocatalytic performance of CPAA doping with different concentrations of Titanium oxide nanocomposite against MB dyes under simulated sunlight irradiations

The pure conjugated polyarylene azomethine (CPAA) and its nanocomposites (CPAA-TiO2) with different concentrations of TiO2 nanoparticles were successfully prepared by in-situ technique and analyzed by different advanced techniques. XRD has confirmed the structural properties and crystallinity of (CPAA) and nanocomposites. The SEM clearly shows that the (CPAA) is uniform and homogeneous, with tightly connected aggregate layers in shape. However, the amount of TiO2 in the nanocomposites greatly affects their morphology, revealing structural differences and indicating a reaction between (CPAA) and TiO2, especially at a higher concentration of 5% TiO2. A new composite of (CPAA) was introduced and the photocatalytic effect for MB was studied. The removal efficiency of (pure-CPAA) over MB dye under simulated sunlight was 62%. However, (CPAA-TiO2 1%) destroyed 90% of MB dyes. It was discovered that the low band gap of (CPAA-TiO2 1% (2.84 eV)) accelerates high electron-hole recombination, increasing photocatalytic activity.

ZnO/ZnS-Polyvinyl Alcohol Hydrogel for Photocatalytic H2-Generation

The separation of nanoparticles from a solution-based photocatalytic reaction is a significant problem in practical applications. To address the issue, we developed a new photocatalyst composite based on ZnO-ZnS heterojunction (ZnOS) embedded in polyvinyl alcohol (PVA) hydrogel, which showed satisfactory results for photocatalyst recycling. PVA-ZnOS composite hydrogel was fabricated by freezing-induced gelation, which enabled the encapsulation of ZnOS nanoparticles into polymeric matrices. PVA hydrogel served as a promising candidate in photocatalytic applications due to its excellent properties such as high transparency, porosity, hydrophilicity, and stability under ultraviolet (UV) light. PVA-ZnOS hydrogel showed worthy activity in H2 generation from Na2S/Na2SO3 aqueous solution under UV radiation with a production rate of 18.8 µmol.h−1. PVA-ZnOS composite hydrogel is a separation-free photocatalyst, which is prospective in a solution-based photocatalytic reactor.

Cyclodextrin-Cross-Linked Hydrogels for Adsorption and Photodegradation of Cationic Dyes in Aqueous Solution

Possessing three-dimensional porous structures and tunable mechanical strengths, cyclodextrin-containing polymeric hydrogels are one of the most promising water-based adsorbent materials due to their easy availability, simple chemical modification and environmental friendliness. In this work, two kinds of hydrogels were prepared via the copolymerization with acrylic acid and vinyl-derivatized β-cyclodextrins in water. These two gels have showed good adsorption performance towards cationic dyes through the noncovalent interactions with their anionic backbones and porous network. Meanwhile, pseudo-second-order model was selected to clarify the adsorption kinetics process. Moreover, nano-scaled TiO₂ was doped into these resultant cyclodextrins-based hydrogels to achieve efficient degradation of dyes upon light irradiation. The obtained TiO₂ -loaded hydrogels could exhibit improved adsorption performance and make the adsorbed dyes photo-degraded with the decolorization rates above 95%. It can be envisioned that such cyclodextrin-based soft materials may find applications in dye clearance and water treatment.

Immobilization of TiO2 Nanoparticles in Hydrogels Based on Poly(Methyl Acrylate) and Succinamide Acid for the Photodegradation of Organic Dyes

Hydrogels have excellent properties that make them ideally suited as host matrices for the immobilization of photoreactive materials such as TiO2 nanoparticles that serve as catalysts in the photodegradation of organic dyes, which is of great importance in practical water pollution treatment applications. However, the application of hydrogels for this purpose remains poorly studied. The present study addresses this issue by developing two types of hydrogels based on poly(methyl acrylate) and succinamide acid with embedded TiO2 nanoparticles for use as photocatalysts in the photodegradation of organic dyes. The results of the analysis demonstrate that the TiO2 nanoparticles are distributed uniformly in the hydrogel matrices, and the hydrogels maintain their original structures after use. The photodegradation efficiencies of the developed TiO2-hydrogels are demonstrated to be reasonably close to that of freely distributed TiO2 nanoparticles in solution for four different organic dyes. In addition, the results of degradation-regeneration cycling tests demonstrate that immobilizing the TiO2 nanoparticles into the hydrogels greatly reduces their loss during utilization, and the photocatalysts can be easily reused. In fact, the two TiO2-hydrogels retain reasonably high photocatalytic degradation performance after four degradation-regeneration cycles.

A π-π stacking perylene imide/Bi2WO6 hybrid with dual transfer approach for enhanced photocatalytic degradation

A new broad-spectrum responsive organic-inorganic hybrid photocatalyst (PI@BWO) was successfully prepared by in-situ growing Bi₂WO₆ nanosheets onto the surface of π-π stacking perylene imide. The obtained PI@BWO hybrids with different composition exhibited enhanced photocatalytic activity for Bisphenol A (BPA) degradation. Among them, 30% PI@BWO exhibited optimal photocatalytic degradation efficiency, which is 2.6 and 3.9 times higher than that of pristine PI and BWO, respectively. Furthermore, PI@BWO also performed good stability and recyclability. Remarkably, the π-conjugation of PI facilitated the separation of charge carriers and improved the utilization of sunlight for PI@BWO. The introduction of BWO nanosheets also enhanced the adsorption capacity for contaminants and provided much more plentiful active sites, promoting the next photocatalytic reaction. Most importantly, PI@BWO could produce abundant reactive species (such as ¹O₂ and ·OH) via the charge carrier transfer and energy transfer dual transfer approach, therefore leading to stronger oxidation ability. The photocatalytic degradation mechanism and pathway of the PI@BWO hybrids were finally proposed. Overall, this present work might provide a new insight into the designing and preparation of efficient organic-inorganic hybrid photocatalysts for environmental-friendly removal of hazardous organic pollutants.

Highly flexible and stable carbon nitride/cellulose acetate porous films with enhanced photocatalytic activity for contaminants removal from wastewater

This study describes the successful fabrication of flexible photocatalytic films to remove contaminants from wastewater, the film is comprising sulfuric acid treated graphitic carbon nitride (SA-g-C₃N₄) embedded within a porous cellulose network (denoted here as CN/CA films). The SA-g-C₃N₄ content in the films was varied from 0 to 50 wt.%. The sulfuric acid treatment introduced carboxyl and sulfonyl groups on the surface of g-C₃N₄, which resulted in strong hydrogen bonding with the hydroxyl groups of cellulose acetate (so strong the partial delimination of the SA-g-C₃N₄ occurred on CN/CA film formation via solvent casting). The obtained films were around 10 μm in thickness, extremely flexible and durable, with the SA-g-C₃N₄ uniformly distributed throughout the cellulose acetate network. The CN/CA films showed excellent activities for aqueous dye degradation under direct sunlight, as well as outstanding performance for photocatalytic reduction of Cr (VI). The photocatalytic activity of the CN/CA films at the optimum SA-g-C₃N₄ content of 50 wt.% was far higher than that of pristine SA-g-C₃N₄, highlighting a main advantage of the composite film fabrication strategy introduced here. Further, the CN/CA films showed excellent stability and reusability, with no loss in activity seen over 5 cycles of dye degradation.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.

Expanded Graphite-Polyurethane Foams for Water-Oil Filtration

Herein, expanded graphite is successfully combined with waterborne polyurethane to develop porous foams with underwater oleophobic properties for the separation of surfactant-free, oil-in-water mixtures and emulsions. To obtain foams with different pore sizes and therefore with different performances in the oil-water filtration process, two solvent-free fabrication processes are adopted. In the first one, the expanded graphite granules are mixed with the waterborne polyurethane (PUEGr), and in the second method, calcium carbonate is introduced to the two-component mixture (PUEGr_t). In both cases, the obtained foams exhibit hydrophilicity and oleophilicity in air and oleophobicity underwater, and they have porous interconnected networks, while their pore size distribution differs significantly. The foams can be used as 3D filters, able to separate, through gravity, surfactant-free, oil-in-water mixtures (10% w/w oil in water) with high oil rejection efficiencies and flow rates that depend on the type of foam. In particular, in the gravity-driven filtration process using 100 mL of the feed liquid, the PUEGr foams have an oil rejection efficiency of 96.85% and flow rate of 9988 L m^-2 h^-1, while for the PUEGr_t foams the efficiency is higher (99.99%) and the flow rate is lower (8547 L m^-2 h^-1) due to their smaller pore size. Although the PUEGr_t foams have slower separation performance, they are more efficient for the separation of surfactant-free emulsions (1% w/w oil in water) reaching an oil rejection efficiency of 98.28%, higher than the 95.66% of the PUEGr foams of the same thickness. The foams can be used for several filtration cycles, as well as in harsh conditions without deteriorating their performance. The nature of raw materials, the simple solvent-free preparation method, the effective gravity-driven filtration even in harsh conditions, and their reusability suggest that the herein engineered foams have great potential for practical applications in oil-water separation through highly energy-efficient filtration.

Robust and anti-fatigue hydrophobic association hydrogels assisted by titanium dioxide for photocatalytic activity

Currently, robust and functional hydrogels have attracted extensive attention due to their potential applications in wastewater treatment, farmland water conservation and other fields. Herein, a series of hydrophobic association hydrogels assisted by titanium dioxide (TiO2) was fabricated via one-pot in situ photo-induced polymerization. TiO2 nanoparticles could act as both photo-initiators and physical crosslinking points. The TiO2-assisted hydrophobic association hydrogels exhibited a high tensile strength of 306 kPa, superior compression strength of 2.17 MPa and excellent fatigue resistance. Simultaneously, the incorporation of TiO2 endowed the hydrogel with photocatalytic capacity for dye wastewater treatment based on the inherent nature of TiO2. The results indicated that the hydrogels contributed to the degradation of various ionic dyes including methylene blue, rhodamine B and bromophenol blue, and the removal of methylene blue achieved a rate of 96.63%. Significantly, the hydrogel could be repeatedly utilized and the removal rate showed no evident decrease after five cycles, indicating that the hydrogels could be powerful candidates as photocatalysts for dye wastewater treatment.

Advanced Design and Synthesis of Composite Photocatalysts for the Remediation of Wastewater: A Review

Serious water pollution and the exhausting of fossil resources have become worldwide urgent issues yet to be solved. Solar energy driving photocatalysis processes based on semiconductor catalysts is considered to be the most promising technique for the remediation of wastewater. However, the relatively low photocatalytic efficiency remains a critical limitation for the practical use of the photocatalysts. To solve this problem, numerous strategies have been developed for the preparation of advanced photocatalysts. Particularly, incorporating a semiconductor with various functional components from atoms to individual semiconductors or metals to form a composite catalyst have become a facile approach for the design of high-efficiency catalysts. Herein, the recent progress in the development of novel photocatalysts for wastewater treatment via various methods in the sight of composite techniques are systematically discussed. Moreover, a brief summary of the current challenges and an outlook for the development of composite photocatalysts in the area of wastewater treatment are provided.

Visible-light photocatalytic capability and the mechanism investigation of a novel PANI/Sn3O4 p–n heterostructure

A novel polyaniline (PANI)/Sn₃O₄ heterojunction composed of PANI nanofibers and Sn₃O₄ nanosheets was fabricated by a facile physical milling technique. Modification of Sn₃O₄ with a PANI conductive polymer contributes to facilitating interfacial charge transfer efficiency, and thus, significantly enhances the visible-light Rhodamine B (RhB) photo-degradation. Results indicate that PANI/Sn₃O₄ heterostructures with 10 wt% PANI reached the maximum degradation efficiency (around 97%) for RhB within 5 h, which is 2.27 times higher than that of Sn₃O₄ alone. This improvement is due to the p–n heterostructure formation in PANI/Sn₃O₄. Moreover, the outcome of reactive species capturing experiments demonstrated that in PANI/Sn₃O₄, holes made the largest contribution to RhB degradation under visible light illumination, while hydroxyl radicals showed less significance under the same conditions. In addition, the photocatalytic mechanism was proposed based on evidence from the reactive species test and energy band structure analysis.

A novel polyaniline (PANI)/Sn₃O₄ heterojunction composed of PANI nanofibers and Sn₃O₄ nanosheets was fabricated by a facile physical milling technique.

Efficient Photocatalytic Degradation of Malachite Green in Seawater by the Hybrid of Zinc-Oxide Nanorods Grown on Three-Dimensional (3D) Reduced Graphene Oxide(RGO)/Ni Foam

A hybrid of ZnO nanorods grown onto three-dimensional (3D) reduced graphene oxide (RGO)@Ni foam (ZnO/RGO@NF) is synthesized by a facile hydrothermal method. The as-prepared hybrid material is physically characterized by SEM, XRD, Raman, and X-ray photoelectron spectroscopy (XPS). When the as-prepared 3D hybrid is investigated as a photocatalyst, it demonstrates significant high photocatalytic activity for the degradation of methylene blue (MB), rhodamine (RhB), and mixed MB/RhB as organic dye pollutants. In addition, the practical application and the durability of the as-prepared catalyst to degradation of malachite green (MG) in seawater are firstly assessed in a continuous flow system. The catalyst shows a high degradation efficiency and stable photocatalytic activity for 5 h continuous operation, which should be a promising catalyst for the degradation of organic dyes in seawater.

Highly efficient pollutant removal of graphitic carbon nitride by the synergistic effect of adsorption and photocatalytic degradation

A novel g-C₃N₄ with strong adsorption capability and efficient photocatalysis activity was prepared by heating urea through a facile method.

BiOBr hybrids for organic pollutant removal by the combined treatments of adsorption and photocatalysis

The xSiO₂–BiOBr (x = 0–5) and SN–SiO₂–BiOBr hybrids were synthesized via a facile one step co-precipitation method. To determine the optimal formula, the photocatalytic degradation of C. I. reactive red 2 (X3B) with xSiO₂–BiOBr (x = 0–5) was investigated. Under simulated sunlight irradiation, 4SiO₂–BiOBr exhibited a better photocatalytic efficiency than other materials; 1.77 and 1.51 times higher than conventional nano TiO₂ and pure BiOBr, respectively. To demonstrate the photocatalytic degradation mechanism, the effect of active species on degradation of X3B was carried out, and a possible degradation pathway was proposed. To realize the combined treatments of adsorption and photocatalysis, an inorganic/organic (I/O) SN–SiO₂–BiOBr hybrid was further strategized and synthesized. It showed much better adsorption performance than the SiO₂–BiOBr composite. It could enrich organic pollutants by facile adsorption, and then degrade them to H₂O and CO₂ under natural sunlight irradiation. Notably, this sunlight-driven photocatalysis can be performed in the slurry resulted from the pollutant adsorption. As a result, the proposed combination of adsorption and photocatalysis will provide a novel strategy to greatly facilitate the treatment of organic wastewater.

The xSiO₂–BiOBr (x = 0–5) and SN–SiO₂–BiOBr hybrids were synthesized via a facile one step co-precipitation method.

A separation-free 3D network ZnO/rGO–rGH hydrogel: adsorption enriched photocatalysis for environmental applications

This study describes the encapsulation of ZnO by reduced graphene oxide to form a composite (ZnO/rGO) that can be incorporated into graphene to form hydrogels (ZnO/rGO–rGH) with three-dimensional (3D) network structures. The unique surface adsorption characteristics of graphene make ZnO/rGO–rGH materials have the ability of fast adsorption and desorption. Meanwhile, the combination of graphene and ZnO nanoparticles can promote the separation efficiency of electrons and holes and improve the photocatalytic activity. The sample showed the highest adsorption-photocatalysis synergistic activity and removed 100% of the BPA (10 mg L⁻¹) within 20 min under UV irradiation. The purification efficiency of ZnO/rGO–rGH can reach more than 90% after 5 rounds of repeated use. We also measured the performance of ZnO/rGO–rGH in removing BPA under flow conditions, and the results showed that this approach with ZnO/rGO–rGH removed 100% of the BPA in 16 h.

Proposed mechanism for photocatalytic BPA degradation by ZnO/rGO–rGH under ultraviolet light illumination.

Metal Phosphides as Co-Catalysts for Photocatalytic and Photoelectrocatalytic Water Splitting

Solar-to-hydrogen conversion based on photocatalytic and photoelectrocatalytic water splitting is considered as a promising technology for sustainable hydrogen production. Developing earth-abundant H₂ -production materials with robust activity and stability has become the mainstream in this field. Due to the unique properties and characteristics, transition metal phosphides (TMPs) have been proven to be high performance co-catalysts to replace some of the classic precious metal materials in photocatalytic water splitting. In this Minireview, we summarize the recent significant progress of TMPs as cocatalysts for water splitting reaction with high activity and stability. Firstly, the characteristic of TMPs is briefly introduced. Then, we mainly discuss the recent research efforts toward their application as photocatalytic co-catalysts in photocatalytic H₂ -production, O₂ -evolution and photoelectrochemical water splitting. Finally, the catalytic mechanism, current existing challenges and future working directions for improving the performance of TMPs are proposed.

Diethylenetriamine-assisted in situ synthesis of TiO2 nanoparticles on carbon nanotubes with well-defined structure and enhanced photocatalytic performance

In solvothermal conditions, DETA will work as a connecting bridge to in situ form TiO₂/CNT composites with a well-defined structure and enhanced photocatalytic performance.

Polyaniline/Carbon Nitride Nanosheets Composite Hydrogel: A Separation-Free and High-Efficient Photocatalyst with 3D Hierarchical Structure

A polyaniline (PANI)/carbon nitride nanosheets (CNNS) composite hydrogel with 3D hierarchical nanostructure is synthesized via in situ polymerization. The 3D hierarchical structure is robust and stable, making the composite hydrogel separation-free and easy to recycling. It is highly excellent in removing organic pollutant for PANI/CNNS composite hydrogel on account of the cooperation of adsorptive preconcentration and the following photocatalytic oxidation. Pollutants are first adsorbed and concentrated into the 3D hierarchical nanostructure of the composite hydrogel. Then the pollutants are in situ oxidized via photocatalysis. The promoted photocatalytic performance can be mainly ascribed to the outstanding interfacial charge separation and photoelectrochemical performance. A new idea of the construction of 3D hierarchical photocatalysts is presented, which can be applied in the sustainability field.