Surfactant Cetyltrimethylammonium Bromide Research Articles

Hierarchical mesoporous zinc-imidazole dicarboxylic acid MOFs: Surfactant-directed synthesis, pH-responsive degradation, and drug delivery

The surfactant template-directed solvothermal method was applied in the synthesis of hierarchical mesoporous zinc-imidazolate derivative metal–organic framework (mesoMOF), which was then utilized for active loading of cisplatin (cis-Pt). To fabricate mesoMOF, various amounts of the surfactant (cetyltrimethylammonium bromide: 0.1–0.3 g) and linker (citric acid: 0.05–0.15 g) were added to the reaction mixture, which resulted in different particle sizes and morphologies. MesoMOF quality attributes such as Specific surface area (SSA), total porous volume, and Barrett-Joyner-Halenda (BJH) pore diameter were also determined. At the optimum reaction condition, mesoMOF with a high surface area (1859 m2/g), pore diameter (14.13 nm) and total pore volume (0.314 cm3/g) was attained. In the next step, cis-Pt was actively loaded in the mesoMOF with a high loading capacity (28% w/w), which was remarkably superior to the microporous MOF. Interestingly, in mildly acidic pH (5.5), mesoMOF underwent degradation, resulting in a rapid release of cis-Pt. Cell viability and apoptosis induction assays confirmed the superiority of the cis-Pt loaded mesoMOF over free drug in a resistant ovarian tumor cell line (A2780cp). Altogether, due to their tunable size and morphology, pH-responsiveness, and acceptable tolerability in mice, the mesoMOFs can be regarded as an anti-cancer drug delivery system.

Nanofluids Characterization for Spray Cooling Applications

In this paper the mathematical and physical correlation between fundamental thermophysical properties of materials, with their structure, for nanofluid thermal performance in spray cooling applications is presented. The present work aims at clarifying the nanofluid characteristics, especially the geometry of their nanoparticles, leading to heat transfer enhancement at low particle concentration. The base fluid considered is distilled water with the surfactant cetyltrimethylammonium bromide (CTAB). Alumina and silver are used as nanoparticles. A systematic analysis addresses the effect of nanoparticles concentration and shape in spray hydrodynamics and heat transfer. Spray dynamics is mainly characterized using phase Doppler interferometry. Then, an extensive processing procedure is performed to thermal and spacetime symmetry images obtained with a high-speed thermographic camera to analyze the spray impact on a heated, smooth stainless-steel foil. There is some effect on the nanoparticles’ shape, which is nevertheless minor when compared to the effect of the nanoparticles concentration and to the change in the fluid properties caused by the addition of the surfactant. Hence, increasing the nanoparticles concentration results in lower surface temperatures and high removed heat fluxes. In terms of the effect of the resulting thermophysical properties, increasing the nanofluids concentration resulted in the increase in the thermal conductivity and dynamic viscosity of the nanofluids, which in turn led to a decrease in the heat transfer coefficients. On the other hand, nanofluids specific heat capacity is increased which correlates positively with the spray cooling capacity. The analysis of the parameters that determine the structure, evolution, physics and both spatial and temporal symmetry of the spray is interesting and fundamental to shed light to the fact that only knowledge based in experimental data can guarantee a correct setting of the model numbers.

The Effect of CTAB on Bentonite for Slow Release Fertilizer

Effect of CTAB (Cetyltrimethylammonium Bromide) surfactant concentration on synthesized CTAB modified bentonite and release of NPK has been studied. Besides, the release kinetic model was also determined. Characterizations of the modified bentonite were done using FTIR (Fourier Transform Infra-Red), XRD (X-Ray Diffraction), and SEM (Scanning Electron Microscope). The amount of released NPK was analyzed using Spectrophotometer UV-Visible and AAS (Atomic Absorption Spectrometer). The release kinetics of NPK were determined using zeroth, first, second, pseudo-first, pseudo-second order, and Korsmeyer-Peppas kinetics models. The result of the study showed that CTAB modified bentonite has been successfully synthesized for NPK slow-release fertilizer. The CTAB concentration in CTAB modified bentonite affects the amount of NPK released out of bentonite and also could reduce the release of NPK. Among modified bentonite synthesized, CMB-3 (bentonite modified by CTAB 2 times CEC of bentonite) could reduce NPK release rate in water very well. The release kinetic of NPK followed the pseudo-second order kinetics model, with the release rate constant (k) of N, P, and K were 0.0027, 0.0540, and 0.0169 g mg−1 day−1, respectively.

The dependence of medium refractive index on optical properties of gold nanorods and their SERS application

In this article, the influence of the medium refractive index on optical properties of gold nanorods (GNRs) and their surface enhanced Raman spectroscopy application were studied. In particular, GNRs have been applied in biomedical sensors to detect diseases by monitoring the changes in the environment. In this study, the changes in optical properties of GNRs were investigated according to the medium refractive index changes in the cationic surfactant cetyltrimethylammonium bromide (CTAB) during synthesis processes as well as GNR dispersion in different medium refractive indices. For instance, in the solutions with different concentrations of CTAB, GNRs were coated by biomolecules [such as PEG, bovine serum albumin (BSA), and glutathione (GSH)], which have different refractive indices. The fundamental reason for the change in optical properties of GNRs is also elucidated. GNRs have been used to enhance surface Raman scattering to detect indigo molecules. The results showed that due to the surface plasmon resonance effect, the GNRs could strongly enhance the scattering signal of indigo dyes, with the lowest detectable concentration of up to 10−8 M and with an enhancement coefficient of over 2000 times.

Surfactant-assisted carbon black for the electrochemical detection of endocrine disruptors

In this paper, the detection performances of carbon black (CB) for bisphenol A (BPA) can be greatly improved by using a surfactant of cetyltrimethylammonium bromide (CTAB). The cyclic voltammetry (CV) behavior of CTAB/CB for BPA can be improved 6 times, compared with CB. The hydrophobicity of the CTAB long-chain alkyl end can enhance the enrichment ability of BPA. Meanwhile, CB can act as an electron transmission bridge to accelerate the electrons transfer to external circuit, thereby improving the sensing signal of CTAB/CB sensor for BPA. The sensor displays a linear range of 0.04 to 0.99 μM, a low detection limit of 0.013 μM and has good reproducibility and selectivity. Finally, the sensor can also be successfully used for detecting BPA in actual samples including tap water and human urine.

Co-intercalation of CTAB favors the preparation of Ti3C2Tx/PANI composite with improved electrochemical performance

With the aid of the amphiphilicity and self-assembly ability of surfactant cetyltrimethylammonium bromide (CTAB), we demonstrate an effective method to increase the interlayer spacing of Ti3C2Tx nanosheets, which is beneficial to improve the performance of composites. Electrochemical tests show that Ti3C2Tx/polyaniline, treated by the co-intercalation of CTAB, exhibits higher redox activity and reversibility. A specific capacitance of 336 F·g−1 for as-prepared Ti3C2Tx/polyaniline composite is achieved at a current density of 0.5 A·g−1, 1.43 times greater than that of common Ti3C2Tx/polyaniline composite (236 F·g−1). Most importantly, a specific capacitance of 135 F·g−1 is retained when the current density increases to 16 A·g−1, much higher than 57 F·g−1 for the common composite. The superior charging/discharging capability is attributed to highly active and reversible polyaniline on Ti3C2Tx as well as the enlarged interlayer spacing, which will provide enough channel for the quick diffusion and migration of electrolyte ions.

A novel carbon nanosphere-based sensor used for herbicide detection

Bentazon (BTZ) is a post-emergence herbicide widely applied in different cultures. It is characterized by low adsorption and high solubility in water, which facilitates its penetration and contamination of aquatic environments. Human exposure to BTZ is responsible for numerous toxic effects and, therefore, it is of great importance to develop simple and efficient analytical methods capable of accurately detecting the presence of this herbicide in environmental samples. The present paper reports the development and application of a glassy carbon electrode modified with carbon nanosphere-based cross-linked chitosan film for the voltammetric determination of BTZ herbicide. The incorporation of cetyltrimethylammonium bromide surfactant into the supporting electrolyte solution helped enhance the voltammetric signal and the sensor repeatability. The use of chitosan film crosslinked with epicholorohydrin contributed toward improving the properties of the carbon nanospheres, including the electron transfer rate. A set of assays were conducted aiming optimizing the experimental parameters related to the supporting electrolyte composition (pH and surfactant concentration) and the square-wave voltammetry technique. Under optimized conditions and based on the application of the method proposed in the study, a linear concentration range of 1.99 to 65.4 μ mol L −1 was obtained, with limit of detection of 1.4 μ mol L −1 and sensitivity of 6.22 A mol −1 L cm −2 . The modified electrode presented good intra- (2.8%, n = 10 ) and inter-day (1.4%, n = 5 ) repeatability and high selectivity for bentazon. The optimized electroanalytical technique was successfully applied for the quantification of bentazon in environmental water samples (recoveries close to 100%). • Nanostructuring a glassy carbon surface for herbicide sensing purposes is reported. • A robust modified electrode is designed by immobilizing carbon nanospheres within a cross-linked chitosan film. • Adsorptive effects from bentazon oxidation products are reduced by applying cetyltrimethylammonium bromide. • The optimized voltammetric sensor was successfully applied for bentazon determination at environmental water samples.

Quasi-cubic hematite with exposed high-energy facets for ethanol gas detection

Facet engineering is a surface optimization strategy to improve the physical and chemical properties of metal oxide semiconductors. To exploit a facile method to fabricate high-performance ethanol sensing material and study the sensing mechanism, a quasi-cubic α-Fe2O3 was investigated, which with high-energy facets exposed. Cetyl trimethyl ammonium bromide (CTAB) surfactant was employed in the preparation of α-Fe2O3 to control the shape and size. The resulting Fe2O3 particles exhibited a mean size of 1.10 µm with high uniformity in size and shape. Additionally, the cubic structure can also optimize the electronic transmission path. Charge carriers are conducting between the cubes required to pass through the electron depletion layer on the surface, as the Fe2O3 particles are separated. Thus, the resistance change of the electron depletion layer significantly affected the overall conductivity. The DFT calculation also confirmed that the exposed facets had high adsorption energy to ethanol molecules, which validated the experimental results. The resulting α-Fe2O3 exhibited an excellent selectivity towards ethanol vapor with a response of 35.14–500 ppm ethanol gas, and the response and recovery times were 12 s and 41 s, respectively. Additionally, the sensing materials exhibited good long-term stability which maintained 92% of its initial response after 60 days, potential using in practical ethanol gas detection.

(−)-Hinokinin antimicrobial agents into functionalized mesoporous silica

The sol–gel process emerges as an interesting strategy to obtain hybrid materials (organic–inorganic materials), it takes place under mild conditions and can produce nanoparticles with different shapes and sizes, leading to composite materials with multifunctional properties. In this paper will describe the synthesis and characterization of the mesoporous silica obtained by the sol–gel process as well as their potential applications as antimicrobial agents, biological markers, odontology, and others. Highly ordered mesoporous silica has gained attention from scientists because it exhibits large specific area and pore volume as well as low density. The preparation of mesoporous silica matrixes via the sol–gel process by using the surfactant cetyltrimethylammonium bromide and the copolymer Pluronic P-123 as structure-driving agents. The results revealed that samples V and VII behaved the most efficiently. Log10 CFU/mL decreased by more than two digits for Candida albicans, Staphylococcus aureus, and Streptococcus mutans and was statistically significant for all the tested microorganisms. Therefore, this study demonstrated that the functionalized mesoporous silica is a viable antimicrobial agent when it is incorporated into dental acrylic resin.

Gold-Modified Micellar Composites as Colorimetric Probes for the Determination of Low Molecular Weight Thiols in Biological Fluids Using Consumer Electronic Devices

This work describes a new, low-cost and simple-to-use method for the determination of free biothiols in biological fluids. The developed method utilizes the interaction of biothiols with gold ions, previously anchored on micellar assemblies through electrostatic interactions with the hydrophilic headgroup of cationic surfactant micelles. Specifically, the reaction of AuCl4− with the cationic surfactant cetyltrimethyl ammonium bromide (CTAB) produces an intense orange coloration, due to the ligand substitution reaction of the Br− for Cl− anions, followed by the coordination of the AuBr4− anions on the micelle surface through electrostatic interactions. When biothiols are added to the solution, they complex with the gold ions and disrupt the AuBr4−–CTAB complex, quenching the initial coloration and inducing a decrease in the light absorbance of the solution. Biothiols are assessed by monitoring their color quenching in an RGB color model, using a flatbed scanner operating in transmittance mode as an inexpensive microtiter plate photometer. The method was applied to determine the biothiol content in urine and blood plasma samples, with satisfactory recoveries (i.e., >67.3–123% using external calibration and 103.8–115% using standard addition calibration) and good reproducibility (RSD < 8.4%, n = 3).

Adsorption complexes ‘zeolite–cationic surfactant’: properties and surface activity in a polymer composite material based on ultra-high-molecular-weight polyethylene

We investigated the adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) to zeolite from premicellar and micellar solutions, as well as some properties of the organically modified zeolite surface and the nature of its interfacial interaction with ultra-high-molecular-weight polyethylene (UHMWPE) in a UHMWPE-based polymer composite material (PCM). The formation mechanism of mono- and bimolecular adsorption layers of cetyltrimethylammonium cation and bromide anion to the clinoptilolite (Cli) surface was proposed, and the thermodynamic and kinetic characteristics of adsorption were determined. The surface texture of organically modified zeolite was studied by instrumental methods; the thermal stability limits of CTAB adsorption layers to zeolite surface and their decomposition behavior in inert and oxidizing media were established. The evaluation of the deformation and strength properties, the study of the supramolecular structure, and the calculation of the thermodynamic and kinetic parameters of the PCM crystallization process revealed that the filing with organically modified Cli increases the UHMWPE surface activity and improves their compatibility.

Evaluating Phospholipid-Functionalized Gold Nanorods for In Vivo Applications.

Gold nanorods (AuNRs) have attracted a great deal of attention due to their potential for use in a wide range of biomedical applications. However, their production typically requires the use of the relatively toxic cationic surfactant cetyltrimethylammonium bromide (CTAB) leading to continued demand for protocols to detoxify them for in vivo applications. In this study, a robust and facile protocol for the displacement of CTAB from the surface of AuNRs using phospholipids is presented. After the displacement, CTAB is not detectable by NMR spectroscopy, surface-enhanced Raman spectroscopy, or using pH-dependent ζ-potential measurements. The phospholipid functionalized AuNRs demonstrated superior stability and biocompatibility (IC50 >200 µg mL-1 ) compared to both CTAB and polyelectrolyte functionalized AuNRs and are well tolerated in vivo. Furthermore, they have high near-infrared (NIR) absorbance and produce large amounts of heat under NIR illumination, hence such particles are well suited for plasmonic medical applications.

Effect of surfactants on the transport of polyethylene and polypropylene microplastics in porous media

The transport of microplastics in porous media is attracting increasing attention. However, to date, research is limited to polystyrene microplastics. Meanwhile, surfactants can promote solid dispersion to form a stable suspension, possibly allowing microplastics to migrate when attached to a surfactant, which would increase the scope and degree of microplastic pollution, further endangering human health and the stability of the ecological environment. Therefore, in this study, the transport behavior of microplastics in porous media was explored in the presence of surfactants. Herein, polyethylene (PE) and polypropylene (PP) were evaluated while dispersed by two ionic surfactants: cationic surfactant-cetyltrimethylammonium bromide (CTAB) and anionic surfactant-sodium dodecylbenzenesulfonate (SDBS). The influence of different factors (surfactant concentration, ionic strength, pH, flow rate, and multivalent cations) on the transport of microplastics in porous media was explored via quartz sand packed-column experiments. Our experimental results show that the transport abilities of PE and PP increased with increasing surfactant concentration when the surfactant concentration was less than the critical micelle concentration (CMC). In the presence of CTAB and SDBS, physicochemical factors had different effects on the transport of microplastics mainly by controlling Zeta potential, advection diffusion and CMC. The mobility of PE and PP decreased with increasing ionic strength, cation valence and pH, and decreasing flow rate. However, the mobility of PE and PP under CTAB is much greater than that of PE and PP under SDBS, because quartz sand can absorb more CTAB molecules through electrostatic attraction to weaken the collision between microplastics and quartz sand. Further, the transport ability of PP was greater than that of PE under all conditions considered. Notably, the Extended-Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory formed by adding osmotic, elastic, and hydrophobic force could well described the migration behavior of microplastics in CTAB and SDBS well. This research highlights that surfactant has a significant impact on the transport ability of microplastics, and provides a comprehensive understanding of the migration and fate behaviors of microplastics affected by surfactants, which is necessary to prevent and reduce the environmental hazards of microplastics.

Fluid state transition mechanism of a ternary component aqueous solution based on dynamic covalent bond

Dynamic covalent bonds are reversible and responsive, the external environment can cause change of molecular configuration of the compound system, leading to changes in the microscopic morphology of the micelles, thereby achieving intelligent control of the fluid state. Therefore, this work used cationic surfactant cetyltrimethylammonium bromide (CTAB), 4-carboxybenzaldehyde (CB) and aniline (NA) to develop a ternary composite fluid state transition system with a molar ratio of 60:40:40 (CTAB/CB/NA). The bottle test method, rheology, 1H NMR, infrared spectroscopy, and Cryo-TEM were used to test and analyze the prepared ternary composite system to explore the effects of different dosages, temperatures and pH values on the rheological behavior of the system. The results show that when the pH increased from 3.13 to 7.25, the CTAB/CB/NA solution changed from a low-viscosity fluid to a transparent gel-like fluid, and the viscosity increased from 1 to 4.6 × 104 mPa·s, and the viscosity recovered when the pH decreased again. Therefore, the reversible changes in the viscoelasticity of the system can be triggered by changing the pH of the CTAB/CB/NA solution. This drastic change in rheological properties is attributable to the pH dependent ionization and formation of dynamic covalent bond CBNA, which is shown microscopically as the morphology of the system micelles changing from spherical micelles to worm-like micelles. The viscosity of the system decreases when the temperature increases, and the viscosity is almost zero when it reaches 50 °C. In addition, by adjusting the pH value, the CTAB/CB/NA solution can obtain more than 3 cycles of morphological changes from spherical micelles to worm-like micelles. This pH-responsive fluid state transition system can meet the viscosity requirements of the oil-displacing agent, and can also reduce the adsorption loss in the formation, and has more valuable research in the field of enhanced oil recovery.

Surfactant-assisted thermal hydrolysis off waste activated sludge for improved dewaterability, organic release, and volatile fatty acid production

The surfactant-assisted thermal hydrolysis pretreatment (THP) of waste activated sludge (WAS) was investigated, focusing on the effect of the surfactant addition on the results of sludge disintegration, dewaterability, organic release, and production of volatile fatty acids (VFAs) via fermentation. Typical anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyl trimethyl ammonium bromide (CTAB) were used for the THP experiments. The supernatant of the THP-treated sludge was anaerobically fermented to determine its potential VFAs yield. The results showed that the surfactant addition, particularly CTAB, enhanced the hydrolysis and organic solubilization of the sludge during THP. CTAB addition led to a 36% increase of dissolved organic and a 27% increase of VFAs production. For the THP-treated sludge with the surfactant addition, its dewaterability was also greatly improved. When the CTAB dosage increased from 0 to 0.10 g/g VSS, the minimum capillary suction time (CST) of the sludge decreased from 205 to 50 s/g TSS, and the sludge particles became smaller and less negative with the zeta potential changing from −12.4 to −8.2 mV. Analysis of extracellular polymeric substances (EPS) of the sludge revealed that the surfactant addition increased the sludge disintegration and organic dissolution during the THP process. The surfactant-assisted THP is shown to be a promising technology to enhance the WAS treatment for improved sludge dewaterability, waste reduction, and resource recovery.

Niosomes modified with cationic surfactants to increase the bioavailability and stability of indomethacin

Niosomes based on the nonionic surfactant Tween 80 and cholesterol and modified with cationic surfactants (cetyltrimethylammonium bromide or its carbamate-bearing analog) were formed by the thin film hydration method. Such a modification of niosomes provides an increase in their ζ potential up to 60 mV, whereas the hydrodynamic diameter of the particles is 100 nm and remains nearly unchanged when the content of the cationic surfactant is varied from 1 to 3 wt.%. The inclusion of anti-inflammatory drug indomethacin in niosomes makes it possible to exceed its limiting solubility in water by nearly 20 times. The dialysis method demonstrated an increase in the release time of the encapsulated drug by 1.5 times, which is a prerequisite for its prolonged action in biosystems. The study of the kinetics of indomethacin cleavage in alkaline media revealed that the niosomes enhanced the stability of the drug providing protection against hydrolytic destruction processes.

Effects of Conformational Variation on Structural Insights from Solution-Phase Surface-Enhanced Raman Spectroscopy.

Surface-enhanced Raman scattering (SERS) spectra contain information on the chemical structure on nanoparticle surfaces through the position and alignment of molecules with the electromagnetic near field. Time-dependent density functional theory (TDDFT) can provide the Raman tensors needed for a detailed interpretation of SERS spectra. Here, the impact of molecular conformations on SERS spectra is considered. TDDFT calculations of the surfactant cetyltrimethylammonium bromide with five conformers produced more accurate unenhanced Raman spectra than a simple all-trans structure. The calculations and measurements also demonstrated a loss of structural information in the CH2/CH3 scissor vibration band at 1450 cm-1 in the SERS spectra. To study lipid bilayers, TDDFT calculations on conformers of methyl phosphorylcholine and cis-5-decene served as models for the symmetric choline stretch in the lipid headgroup and the C═C stretch in the acyl chains of 1,2-oleoyl-glycero-3-phosphocholine. Conformer considerations enabled a measurement of the distribution of double-bond orientations with an order parameter of SC═C = 0.53.

Time dependent physicochemical changes of SDS-CTAB interacted self assembled vesicles: Ostwald ripening effect

It is found that oppositely charged surfactants SDS (sodium dodecyl sulfate) and CTAB (cetyltrimethylammonium bromide) at low concentrations (< critical micelle concentration or CMC) interact, and form self-assemblies (vesicles) in aqueous medium. Physicochemical characterization of the assemblies has been studied and reported. It has been found that the characteristic properties of these assemblies change with time. Investigations on the time dependent changes of such vesicles have been monitored over a period of three months. The properties studied were, turbidity, surface tension, conductance, size and shape, ζ-potential, fluorescence anisotropy and quenching of photosensitive dyes in them, thermodynamics of formation as well as toxicity. The surfactants (well below their CMCs) were mixed in different proportions making the final concentration of all at 0.6 mM. They were kept at temperature 303 K, and examined at different times (on the day of mixing, and subsequently after 10, 30, 60, and 90 days). It is known that by the phenomenon of Ostwald Ripening (OR) process, morphological changes in colloidal solution takes place; larger particles grow in size with time at the expense of smaller particles.We studied the OR effect on the physicochemical properties of the growing SDS-CTAB interacted vesicles in aqueous medium. Results and their documentations are herein presented. Such an elaborate study of vesicles with reference to OR process as per our knowledge was not done in the past.

Unravelling the role of Ag[sbnd]Cr interfacial synergistic effect in Ag/Cr2O3 nanostructured catalyst for the ammoxidation of toluene via low temperature activation of Csp3-H bond

An environmentally benign and cost-effective synthesis of benzonitrile is reported by direct oxidative cyanation of aromatic Csp3-H bonds of toluene over Ag(I)/Cr2O3 nanostructured catalyst. The catalyst was prepared by a hydrothermal route using cationic surfactant cetyltrimethylammonium bromide and was characterized by powder XRD, XPS, SEM, TEM, TGA, TPD, TPR, UV-visible, FTIR, XANES, and ICP-AES methods. Conjugal effect of Lewis plus Brønsted acidity coupled with AgCr interfacial synergistic interaction appears as detrimental for its high catalytic activity and selectivity (98.4%) for benzonitrile. In situ DRIFTS analysis suggested that the catalytic system proceeded via a reaction pathway explained by Mars-van Krevelen mechanism.

“Bi–O” vacancy-pairs induced photochromic behavior in Bi2WO6 ultrathin nanosheets

Developing cheap and efficient materials for enhancing the photochromic performance upon visible or solar light irradiation is a hot-topic in the field of solar energy conversion. However, few inorganic photochromic materials can provide satisfying applications due to their low coloring and bleaching efficiency as well as slight color change. Here, we synthesized the bismuth tungstate (Bi2WO6) ultrathin nanosheets with the thickness of 1.29 nm via co-precipitation-hydrothermal method using cetyltrimethylammonium bromide (CTAB) surfactant. The prepared ultrathin nanosheets show the similar crystalline structure but a narrowed band gap of 2.73 eV, as compared with the 2.86 eV of pristine Bi2WO6. Additionally, the numerous [WO6–xBr2x] species and abundant “Bi–O″ vacancy pairs on the surface can serve as active sites that suppress the recombination of photogenerated electron-hole pairs and capture the photogenerated electrons to form the color trapping centers. As a result, Bi2WO6 ultrathin nanosheets exhibit excellent photochromic behavior upon solar light irradiation (coloring time of 5 s) and under dark atmospheric treatment (bleaching time of 35 min) compared with WO3-based photochromic materials (coloring time of 20–60 min and bleaching time of 3 h days).