Photoreaction Rate Research Articles

Anchoring TiO2 and CuO nanoparticles on SnO2 nanotube arrays to construct ternary heterostructure for visible-light-driven photocatalytic degradation of green malachite dye

Designing and constructing heterostructure photocatalysts is necessary to facilitate the long-term separation of photogenerated charge carriers and enhance photocatalytic efficiency. Herein, a ternary nanocomposite photocatalyst based on SnO2, TiO2 and CuO semiconductors was successfully synthesized and employed as a highly effective photocatalyst for the malachite green (MG) dye degradation under visible light irradiation. According to the results, the ternary SnO2/TiO2/CuO nanocomposite demonstrated impressive photocatalytic activity (98.4 %) compared to pristine SnO2 nanotubes (40.3 %), binary SnO2/TiO2 (76 %) and SnO2/CuO nanocomposites (88 %), when exposed to 90 min of visible illumination. The photoreaction rate constant of SnO2/TiO2/CuO nanocomposite (0.0482 min−1) was found to be ∼8.5 times faster than SnO2 nanotubes (0.0057 min−1) against MG dye. This enhancement in photocatalytic performance can be attributed to the introduction of TiO2 and CuO which effectively suppress the recombination of photogenerated electron-hole pairs, accelerate the transfer of charge carriers, increase the active sites, and improve the optical absorption properties. Scavengers were used to elucidate the photocatalytic mechanism, exhibiting the pivotal role of •O2− and h+ in the photodegradation process. Besides, recyclability tests showed acceptable results after four cycles, confirming the stability and durability of the SnO2/TiO2/CuO nanocomposite against RhB dye degradation.

Kinetic study of photoreactions in an automatic single-liquid-slug oscillatory flow platform

Herein, an automatic single-liquid-slug oscillatory flow platform was established for the kinetic investigation of photochemical reactions. Reaction parameters including concentration, reaction time, light intensity, pressure, and temperature were controlled precisely in an automatic manner, and the reaction outcomes were obtained accurately via, integration of an online HPLC. With the reaction kinetics measurement performed for the photocatalytic oxidation of citronellol by Ru(bpy)3Cl2 at a volume scale of 50 μL, it was demonstrated that the single-liquid-slug oscillatory flow method was capable of achieving material and time savings of 70 % and 38 % respectively as compared to the conventional batch method, and of 80 % and 62 % respectively as compared to the continuous flow method. The four reaction orders manifesting the effects of the substrate concentration, photocatalyst concentration, light intensity, and oxygen pressure, respectively, were attained as well as the photoreaction rate constant. Furthermore, the kinetic data obtained under a series of temperatures also shed light on the photoreaction mechanism which exhibited a relationship between the photoreaction rate constant and temperature that deviated from the Arrhenius law. The approach developed in this work is especially useful for the kinetic studies of photoreactions with relatively slower intrinsic reaction kinetics, achieving a more resource-efficient practice with higher repeatability and accuracy.

Facile preparation of mesoporous NiS-coupled Co3O4 nanocomposites for photocatalytic reduction of Cr(VI) ions under visible light illumination

Cr(VI) ion deposits in water can negatively affect the ecosystem and people's health. Constructing a reusable and effective photocatalyst defies dominating semiconductors' unstable nature and rapid recombination. Here, with variable NiS contents, new sol-gel nanocomposites of mesoporous NiS–Co3O4 were synthesized. We investigated the photocatalytic performance of NiS nanoparticles (NPs) anchored to mesoporous Co3O4 in the photoreduction of Cr(VI) ions under visible illumination. The structural, textural, and optical features of the synthesized materials were completely characterized by different techniques. The constructed nanocomposites demonstrated mesostructured materials with 133–160 m2/g of surface area. Changing the NiS content revealed the diminution in bandgap (Eg) from 2.46 to 1.8 eV and hence Co3O4's ability to absorb visible light was altered. The 2.0 gL-1 of 12 wt% NiS–Co3O4 photocatalyst demonstrated superior photoreduction efficiency of Cr(VI) ions with a photoreaction rate of 0.0583 min−1 after 50 min of illumination. Moreover, this photocatalyst revealed effective photocatalytic stability and retained 97 % of its original performance after 5 cycles. The enhancement in performance of this NiS–Co3O4 nanocomposite is mainly due to modified light absorption and potent interfacial isolation of charge carriers.

Reasonable decoration of CuO/Cd0.5Zn0.5S nanoparticles onto flower-like Bi5O7I as boosted step-scheme photocatalyst for reinforced photodecomposition of bisphenol A and Cr(VI) reduction in wastewater

Building S-scheme heterostructures is a sophisticated approach to receiving outstanding catalysts for environmental detoxification. Herein, ternary CuO/Cd0.5Zn0.5S/Bi5O7I (CO/CZS/BOI) nanocomposites were constructed by in-situ decorating of CuO and Cd0.5Zn0.5S nanoparticles onto Bi5O7I micro-sphere in a facile route. The optimal CO/CZS/BOI reflected reinforced bisphenol A (BPA) photo-oxidation (95% in 70 min) and Cr(VI) photo-reduction (96.6 in 60 min) under visible light. Besides, CO/CZS/BOI afforded 5.10 (4.44), 4.42 (3.71), and 6.60 (5.27) fold reinforcement in the BPA (Cr(VI)) photo-reaction rate compared to BOI, CZS, and CO, respectively. This behavior was linked to the development of S-scheme mechanisms resulting from the co-effects of BOI, CZS, and CO in retaining the optimum redox capacity, facilitating the dissolution of photo-carriers, increasing reactive sites, and strengthening the visible-light response. The parameters influencing the catalytic reaction of CO/CZS/BOI, such as light intensity, catalyst dosage, and pH, were deeply studied. The quenching tests declared the prominent roles •O2− and •OH in the breaking down of BPA and the participation of electrons and •O2− in the photocatalytic conversion of Cr(VI). The cyclic tests verified the robust photostability of CO/CZS/BOI, which is associated with the reintegration process between the free h+ coming from CZS and the photo-induced e– of CO and BOI in the S-scheme system. In conclusion, the present study provides a profound understanding of the photo-reaction mechanism of CO/CZS/BOI and introduces a novel concept for constructing a superior dual-Scheme system for efficient wastewater detoxification.

Enhanced photodegradation of p-arsanilic acid by oxalate in goethite heterogeneous system under UVA irradiation.

The widespread used organoarsenicals have drawn attention for decades due to their potential environment risks. In this study, a heterogeneous system of goethite/oxalate irradiated using UVA light (λ = 365 nm) was applied for the removal of ASA, a kind of organoarsenicals used in animal feeding operations as additives, from the aqueous phase through photodegradation. Results showed that the presence of 5 mM of oxalate significantly enhanced the photodegradation efficiency of ASA in the 0.1 g/L of goethite suspended system from 28 to ~100% within 180 min reaction at pH 5. Acid conditions favored the photoreaction rate, compared with neutral and basic conditions. This reaction process was also influenced by the initial concentration of oxalate and ASA. Furthermore, the mechanism study was conducted by quenching experiments and revealed the important roles of·OH in the degradation of ASA in the goethite/oxalate/UVA system. By analyzing the reaction products, both inorganic arsenic (As(III) and As(V)) and ammonia were detected during the photodegradation of ASA. These findings help to gain a better understanding of the geochemical behavior of ASA in surface water and can also provide a potential treatment method for the organoarsenicals contaminated water.

Green synthesis of stable CuFe2O4/CuO-rGO heterostructure photocatalyst using basil seeds as chemo-reactors for improved oxytetracycline degradation

Complex structures of pharmaceutical antibiotics prevent their natural degradation by traditional remediation strategies, resulting in persistent environmental pollution and reproduction of destructive bacteria, that pose hazardous human health consequences. As a workaround, basil seed biomass resource-derived CuFe2O4/CuO-graphene like carbon S-scheme heterostructure, aiming to eliminate the oxytetracycline (OTC) antibiotic in a persulfate activation helical plug flow photoreactor (HPFPR), is developed via a hydrothermally coupled pyrolysis approach. The champion CuFe2O4/CuO-graphene like carbon manifests the best photo-degradation efficiency (87.49% within 90 min) with the photoreaction rate constant of 0.0495 min−1 for OTC degradation. The desirable photo-degradation efficiency was assigned to the higher visible-light absorbance, built-in interfacial electric field and reduced recombination of charge carriers, and superior redox capability due to the S-scheme heterojunction. The HPFPR's performance was verified by a 3D computational fluid dynamics (CFD) model and central composite design (CCD). As proposed CuFe2O4/CuO-rGO demonstrated significant reusability and stability owing to the presence of a carbon shell. The scale-up in-situ synthesis of environmentally friendly, large-scale metal oxide heterojunctions in natural carbon supports offer novel insights in photocatalytic production for promising water treatment applications.

Calcium Oxide Nanoparticle Production and its Application as Photocatalyst

This study aimed to synthesize and characterize calcium oxide (CaO) nanoparticles as a photocatalyst in the degradation process of indigo carmine (IC) dyes. Several steps were carried out to produce CaO nanoparticles by mixing 0.5 M of CaCl2 solution with various NaOH solutions (0.5; 0.8; and 1.0 M). Experimental results showed the prospective control of CaO particle sizes. The experiments also confirmed that the greater concentration of NaOH correlates with the greater yield of nanoparticles produced. The best condition to produce CaO nanoparticles was obtained when using the ratio of CaCl2: NaOH of 1:2. Additional results showed the difficulties in the production of CaO particles in the nanometer size, which is due to the existence of solid agglomeration, giving ideas to the need in putting some additional experimental steps. The photocatalytic degradation studies showed several factors affecting the photoreaction rate, including processing time, catalyst dosage, and dye concentration. CaO nanoparticles had the best performance in catalyzing indigo carmine in 50 minutes, which was shown by the combination of 10 mg of CaO nanoparticles and 80 ppm of dye concentration.

Molecular engineering of biomimetic donor-acceptor conjugated microporous polymers with full-spectrum response and an unusual electronic shuttle for enhanced uranium(VI) photoreduction

Realizing an efficient photochemical uranium reduction process using metal-free conjugated polymers is highly desirable, but is extremely challenging, as it requires a broad photo-response range and efficient electron transmission channels. Herein, three novel full-spectrum (200 ≤ λ ≤ 800 nm) responsive biomimetic donor–acceptor conjugated microporous polymers (CMPs) were successfully constructed to photoreduce uranium through a molecular engineering strategy. The optical band gap and built-in electric field of the CMPs were conveniently optimized via various quinone-containing acceptors. Furthermore, the quinone-containing block exhibited outstanding redox activity, which could serve as an unique electron shuttle to rapidly transfer electrons. Consequently, ECUT-TQ with 2,6-dibromobenzo[1,2-b:4,5-b']dithiophene-4,8-dione block exhibits a narrow band gap as low as 1.70 eV, a stronger built-in electric field and more efficient charge separation, achieving 97.4% photocatalytic U(VI) reduction efficiency with a photoreaction rate constant of 0.057 min−1. The exhaustive mechanism analysis illustrates that the dominant active species in the photocatalytic process where U(VI) is reduced to UO2 are photoelectrons and •O2– radicals. This work provides a novel approach for designing high-performance green biomimetic photocatalysts for removing radioactive pollution.

A novel organic/inorganic S-scheme heterostructure of TCPP/Bi12O17Cl2 for boosting photodegradation of tetracycline hydrochloride: Kinetic, degradation mechanism, and toxic assessment

The exploration of environment-friendly and efficacious materials with eminent photocatalytic efficacy is critical for the elimination of pharmaceutical antibiotics. Herein, a visible-light-driven organic–inorganic S-scheme heterostructure of meso-tetra (4-carboxyphenyl) porphyrin (TCPP)/Bi12O17Cl2, aiming to wipe out the antibiotic in wastewater, is developed via a simple approach. The TCPP is anchored on the surface of Bi12O17Cl2 to create the S-scheme junction between TCPP and Bi12O17Cl2, which strengthens visible-light response and expedites the spatial disintegration and conservation of photo-carriers with high redox capacity, therefore leading to a significant reinforcement of the photo-activity and stability. The champion TCPP/Bi12O17Cl2 manifests the best photo-degradation efficiency of 79.4% with the photoreaction rate constant of 0.0125 min−1 for tetracycline elimination, being 2.6 folds that of Bi12O17Cl2. The involved crucial reactive radicals, photo-degradation pathway and mechanism, and the eco-toxicity of intermediates over TCPP/Bi12O17Cl2 were elucidated through scavenging tests, LC-MS analysis, and toxicity calculation. This research illustrates the potential practicability on the rational design of porphyrin-based S-scheme heterojunction photocatalysts for efficient antibiotic removal.

Fast photocatalytic oxidation of ciprofloxacin over Co3O4@CeO2 heterojunctions under visible-light

Background: The widespread dispersal of antibiotic waste in freshwater has accelerated the water contamination that impacts the ecosystem. Moreover, different studies have discussed the expected green mineralization of such contaminants. Methods: Herein, a unique Co3O4@CeO2 nanocomposite was developed by incorporating different doses (5–20 wt%) of Co3O4 nanoparticles (NPs) using a surfactant-based sol–gel/ calcination technique. The photocatalytic activity of Co3O4@CeO2 nanocomposites was estimated in the degradation of ciprofloxacin (CIP) antibiotic under visible exposure. Significant finding: Optimizing the Co3O4 mass yields a bandgap semiconductor of 2.66 eV with a wide visible light. The 15% Co3O4@CeO2 nanocomposite displayed the best CIP destruction performance after 45 min, with 2-fold greater activity than pure CeO2 NPs. After 30 min of visible light illumination, 2.4 gL−1 dosage of 15% Co3O4@CeO2 achieved complete CIP oxidation with a photoreaction rate of 0.12 min−1 and retained significant reusability after five runs. The explanation for the improved photocatalytic efficiency of the Co3O4@CeO2 is postulated based on the effective segregation of photoinduced charge carriers via an S-scheme mechanism, where electron–hole pairs can easily move between CeO2 and Co3O4 because of their matched band locations. This research corroborates the use of nanoheterojunction oxides in rapidly removing antibiotic residues under visible light.

A nearly complete decomposition of MO, TC and OFX over a direct Z-scheme p-n heterojunction g-C3N4/La-Bi2O3 composite

To find a photocatalyst for photodegrading different pollutants, a direct Z-scheme p-n heterojunction g-C3N4/La-Bi2O3 (LBOCN) composite was prepared in this study. The composite was characterized by XRD, SEM, HRTEM, UV–vis DRS, M-S, XPS, EIS and PL. The photocatalytic activity of LBOCN was evaluated by photodegrading methyl orange (MO), ofloxacin (OFX) and tetracycline (TC). Many nanodots in the as-prepared LBOCN were clearly observed in the HRTEM images, which could drastically accelerate the transfer of photogenerated charges since their size is 4–5 nm, shortening the transfer route of photogenerated carriers from the inner part to the outside. The p-n junction strengthened the Z-scheme to separate the photogenerated electrons and holes, therefore improving the photocatalytic property of LBOCN. In the photodegradation of MO, the photoreaction rate of LBOCN is approximately 13 times that of Bi2O3 (BO), 12 times that of g-C3N4 (CN), 3 times that of La-Bi2O3 (LBO) and 2 times that of g-C3N4/Bi2O3 (BOCN). Moreover, LBOCN can also completely photodegrade OFX within 60 min. Finally, this work demonstrates if a p-n-type Z-scheme heterojunction structured composite can generate superoxide radicals or hydroxyl radicals under light irradiation, the refractory antibiotics, such as ofloxacin, can be completely decomposed into small molecules under the synergistic effects of effective separation of photogenerated electron-hole pairs driven by the p-n junction and strong redox ability of the photogenerated carriers.

Visible-light photooxidation of ciprofloxacin utilizing metal oxide incorporated sol-gel processed La-doped NaTaO3 nanoparticles: A comparative study

The supper dissemination of antibiotic waste in water resources has exponentially progressed the vital water and soil pollution that affect human health and the environment. Consequently, there have been several types of research anticipated for the green mineralization of such pollutants. Herein, we intended a surfactant-aided sol-gel formation of lanthanum-doped sodium tantalate (LNTO) nanocrystals. The synthesized 13 nm averaged-size perovskite LNTO nanocrystals were responsive to visible-light irradiation by incorporation of 4.4–5.2 nm oxide nanoparticles, namely Bi2O3, CdO, Fe2O3, and CuO at 4.0 wt% through coprecipitation. The formed nanomaterials unveiled mesostructured surface textures with specific surface areas of 199–229 m2 g−1. The obtained nanoceramics were employed for the mineralization of 10 ppm of ciprofloxacin antibiotic (CPF) as an emerging antibiotic waste in water under visible light irradiation. The CuO-incorporated LNTO exhibited the best photocatalytic oxidation of CPF after 120 min compared with other oxides with an excellent photoreaction rate of 0.0343 min−1 which is 49 times higher than the pure LNTO. The 2.0 gL−1 CuO/LNTO-dose achieved the full photooxidation of CPF at an oxidation speed of 0.0738 min −1 within just 1.0 h of visible light irradiation and magnificent regeneration ability. This enhanced activity of CuO/LNTO is regarded as significant light absorption and a bandgap energy reduction to 2.12 eV. Besides that, the heterojunction between CuO and LNTO amended the photogenerated carrier mobility and separation as concluded from the photoluminescence and photocurrent exploration. This comparative work suggests the proper design of low bandgap oxide decoration of solution-based perovskite oxide photocatalysts for promoting the visible-light mineralization of antibiotics in water.

Bi2WO6/SiC composite photocatalysts with enhanced photocatalytic performance for dyes degradation

Bi2WO6 demonstrates the limited photocatalytic activity due to its high photoelectron recombination rate. However, its photocatalytic performance is expected to be improved by forming Step-scheme (S-scheme) heterojunction and SiC is a potential candidate because of its high electron transfer rate in photocatalytic process. In this study, S-scheme heterojunction Bi2WO6/SiC nanocomposites were synthesized by simple hydrothermal method, and their photo degradation properties for rhodamine B (RhB) under visible light were studied. The results show that silicon carbide nanoparticles have been successfully deposited onto the petal-microsphere shaped Bi2WO6 phase. The nanocomposite with mole ratio of Bi2WO6 to SiC of 1:1 exhibits the highest photo degradation rate as tested in the photocatalytic experiments. The photoreaction rate of the nanocomposite is 3.7 times higher than that of pure Bi2WO6 and 15.5 times higher than that of pure SiC, and the nanocomposite demonstrates good photocatalytic stability.

Selective and Cooperative Photocycloadditions within Multistranded Aromatic Sheets

A series of aromatic helix-sheet-helix oligoamide foldamers composed of several different photosensitive diazaanthracene units have been designed and synthesized. Molecular objects up to 7 kDa were straightforwardly produced on a 100 mg scale. Nuclear magnetic resonance and crystallographic investigations revealed that helix-sheet-helix architectures can adopt one or two distinct conformations. Sequences composed of an even number of turn units were found to fold in a canonical symmetrical conformation with two helices of identical handedness stacked above and below the sheet segment. Sequences composed of an odd number of turns revealed a coexistence between a canonical fold with helices of opposite handedness and an alternate fold with a twist within the sheet and two helices of identical handedness. The proportions between these species could be manipulated, in some cases quantitatively, being dependent on solvent, temperature, and absolute control of helix handedness. Diazaanthracene units were shown to display distinct reactivity toward [4 + 4] photocycloadditions according to the substituent in position 9. Their organization within the sequences was programmed to allow photoreactions to take place in a specific order. Reaction pathways and kinetics were deciphered and product characterized, demonstrating the possibility to orchestrate successive photoreactions so as to avoid orphan units or to deliberately produce orphan units at precise locations. Strong cooperative effects were observed in which the photoreaction rate was influenced by the presence (or absence) of photoadducts in the structure. Multiple photoreactions within the aromatic sheet eventually lead to structure lengthening and stiffening, locking conformational equilibria. Photoproducts could be thermally reverted.

Semiconducting Metal–Organic Frameworks Decorated with Spatially Separated Dual Cocatalysts for Efficient Uranium(VI) Photoreduction

AbstractReduction of soluble hexavalent uranium (U(VI)) to sparingly soluble tetravalent uranium (U(IV)) with semiconductor photocatalysts is recognized as a novel, green, and simple U‐extraction method. Furthermore, effective charge separation and utilization are critical factors to achieve high‐efficiency U(VI) photoreduction. Herein, a UiO‐66‐based heterostructured photocatalyst (MnOx/UiO‐66/Ti3C2Tx) with spatially separated dual cocatalysts (MnOx nanoparticles and Ti3C2Tx MXene nanosheets) is successfully developed for efficient U(VI) photoreduction without sacrificial agents. As co‐catalysts, MnOx nanoparticles favor the trapping of holes, while Ti3C2Tx MXene nanosheets tend to collect electrons. Consequently, the photogenerated holes and electrons flow into and out of the photocatalyst, respectively, achieving efficient charge separation required by MnOx/UiO‐66/Ti3C2Tx to remove U(VI). Impressively, the U(VI) removal ratio via MnOx/UiO‐66/Ti3C2Tx reaches to 98.4% in the U(VI) solution after 60 min, with a photoreaction rate constant of 0.0948 min−1. Moreover, MnOx/UiO‐66/Ti3C2Tx exhibits brilliant U(VI) extraction capacity in various U(VI) wastewater and U(VI)‐spiked real seawater. Further mechanistic studies indicates that the photogenerated electrons are transferred from the conduction band of UiO‐66 to Ti3C2Tx MXene to reduce U(VI) and generate ·O2–, further leading to a stable crystal phase of (UO2)O2·2H2O. Furthermore, the photogenerated holes are extracted by MnOx nanoparticles in MnOx/UiO‐66/Ti3C2Tx to oxidize water.

Solar light-responsive CdS/UiO-66-NH2 for ultrafast uranium reduction from uranium-containing mine wastewater without external sacrificial agents

• 40 CUN achieved a record kinetic reaction rate reduction efficiency in air atmosphere and absence of sacrificial agents; • Cd 2+ ions are absorbed on UiO-66-NH 2 by the coordination bonds of Cd-N. • The photogenerated holes are consumed by oxidizing S 2− to SO 4 2− . • 85.62% of U(VI) in the uranium contained real mine wastewater could be removed under solar. As the nuclear industry ushered in a historical opportunity for rapid development, the massive discharge of nuclear waste liquids posed health risks to humans and environmental pollutant due to its combined chemotoxicity and radiotoxicity. Therefore, how to effectively treat uranium-containing mine wastewater is full of challenges. In this work, the CdS/UiO-66-NH 2 nanoparticles photocatalysts were prepared and applied for reduction of uranium hexavalent in the absence of any sacrificial agents. The kinetic photoreaction rate reaches 3.78 mmol/(g·h), which is a record among the reported rate. Excitingly, 85.62% of U(VI) in the mine wastewater could be removed under sunlight irradiation in the air condition. The results show that the photogenerated electrons rapidly transport from CdS to UiO-66-NH 2 due to the formation of heterojunction structure, whereas the photo-generated holes are consumed by oxidizing S 2− to SO 4 2− . This work represents an important step towards the remediation of the radioactive environment from mine wastewater, and promotes the extensive application of photocatalysis technology.

Photoactivity enhancement of La-doped NaTaO3 nanocrystals by CuO decoration toward fast oxidation of ciprofloxacin under visible light

The use of antibiotics has increased over recent years owing to the spread of infections worldwide. The spread of this toxic matter, especially in water, has become crucial to public health and the environment. Accordingly, there has been extensive research, and numerous approaches have been proposed for the eco-friendly elimination of antibiotic contaminants. In this study, we designed a solution-based synthesis of La-doped NaTaO3 crystals, which become visible-light-responsive photocatalysts upon decoration with 1.0–4.0 wt% CuO nanoparticles. CuO/LNTO exhibited a mesoporous texture and large specific surface areas in the range 199–221 m2 g−1 compared to 230 m2 g−1 for pure LNTO. Tuning the CuO content in LNTO provides a material with a broad absorbance in the visible range and a prominent attenuation of the bandgap energy from 4.05 to 2.1 eV at CuO content of 3.0 wt%. CuO/LNTO was used for the photodegradation of ciprofloxacin as a nascent antibiotic model. The 2.0 gL−1 dose of 3%-CuO/LNTO accomplished total oxidation of CPF with photoreaction rate of 0.071 min−1 in water after 60 min visible light illumination and maintained substantial recyclability of five cycles. The high photooxidation activity of CuO/LNTO is ascribed to the formation of a heterojunction between CuO and LNTO. The heterojunction improved the photoinduced charge separation and mobility, as confirmed by the photoluminescence and photocurrent studies. This novel study proposes that the decorated sol-gel produced perovskite oxide nanostructures are promising photocatalysts is for the fast elimination of antibiotic contaminants under visible light.

Photochemical-induced phase transitions in photoactive semicrystalline polymers.

The emergent photoactive materials obtained through photochemistry make it possible to directly convert photon energy to mechanical work. There has been much recent work in developing appropriate materials, and a promising system is semicrystalline polymers of the photoactive molecule azobenzene. We develop a phase field model with two order parameters for the crystal-melt transition and the trans-cis photoisomerization to understand such materials, and the model describes the rich phenomenology. We find that the photoreaction rate depends sensitively on temperature: At temperatures below the crystal-melt transition temperature, photoreaction is collective, requires a critical light intensity, and shows an abrupt first-order phase transition manifesting nucleation and growth; at temperatures above the transition temperature, photoreaction is independent and follows first-order kinetics. Further, the phase transition depends significantly on the exact forms of spontaneous strain during the crystal-melt and trans-cis transitions. A nonmonotonic change of photopersistent cis ratio with increasing temperature is observed accompanied by a reentrant crystallization of trans below the melting temperature. A pseudo phase diagram is subsequently presented with varying temperature and light intensity along with the resulting actuation strain. These insights can assist the further development of these materials.

Couple of graphene oxide and functionalized carbon nanotubes for dye degradation enhancement of anatase under visible light and solar irradiation.

Graphene oxide sheets (GO) were coupled with carbon nanotubes (CNTs) to enhance the photoactivity of anatase under visible and solar irradiation. The carbon nanotube surface was functionalized in the acidic reflux condition before coupling with GO and decoration of anatase by the sol-gel method. A modified kinetic model was appropriately applied to predict the breakthrough in the methylene blue degradation yield and determine the constant rate which was clearly affected by coupling architecture. The nanocomposite fabricated by the same proportions of GO and CNTs, 3.33%, exhibited the maximal degradation yield, 96.5%, in the dye solution with the initial concentration of 3.0 mg l-1. The characterizations based on X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and field emission scanning electron microscopy (FESEM) revealed that the functionalized CNTs could create the appropriate space between the graphene sheets for uniformly interconnection of anatase via oxygen-containing groups onto the material surfaces. This enhancement in the degradation efficiency could be ascribed to the unique architecture, leading to a decrease in bandgap energy, 2.2 eV, which facilitated the electron-hole separation. Besides of breakthrough in the photoreaction rate, the adequate architecture led to an efficient reduction in the content of carbon-based materials. Also, the performance of mentioned nanocomposite under sunlight photons was effectively higher than that under UV irradiation. The hybrid nanocomposite provided a large number of active sites for photoreactions to facilitate the treatment of wastewater under solar irradiation.

A holistic approach for anthracene photochemistry kinetics

Laser-induced reversible photocycloadditions with anthracene monomer (A) are of key interest in generating light responsive materials. Upon dimerization (forward reaction) these species form dimers A2 that can be cleaved to regenerate the monomer A (reverse reaction). Thus, if such moieties are incorporated in a polymer network, light-shaping of the material properties becomes possible. The photocycloaddition of A is mostly displayed as a simple wavelength (λ) gated on/off switch with long UV light inducing bond formation and short UV light bond cleavage. However, the real situation is far more complex as the forward and reverse reactions are concomitantly initiated in the shorter λ regime and their competition is strongly influenced by the reaction conditions. Herein, we report a λ dependent kinetic study to determine the forward and reverse photochemical reactivity, which can serve as a blueprint to design large-scale polymeric network materials. We introduce fundamental photoreaction rate laws for cases of exclusive dimerization, exclusive dimer cleavage, and competitive absorption and reactions. The λ-dependent kinetic parameters are determined based on a protocol covering dedicated short timescale experiments under specific conditions, either starting with a dominant presence of A or A2. Model validation is performed using long time scale irradiation experimental data. In particular, the λ region between 260 and 330 nm is explored to determine the optimum λ for A2 cleavage and to showcase the concentration variations of A and A2 at various λ, including both situations of reactant depletion and equilibrium settlement.