BiOBr TiO2 Research Articles

One-step synthesis of oxygen vacancy-rich BiOBr/TiO2 composite: Ultrafast adsorption-photocatalytic performance and mechanism

A novel 3D bird’s nest-like BiOBr/TiO2 (BT) composite with abundant reactive sites and large specific surface area was synthesized via a one-pot solvothermal method. The unique 3D structure endowed with BiOBr nanosheets on its surface can interconnect and coat with metastable TiO2 nanoparticles, which established a compact electron transport pathway. When exposed to visible light, BT showcased a remarkable RhB (50 mg/L) removal efficiency of 100.00 % within only 10 min. Meanwhile, BT showed an ultra-high reaction rate constant of 0.63 min−1, which was 16.15 and 87.50 times higher than those of single-component BiOBr and TiO2, respectively. BT also exhibited exceptional reusability and maintained over 99.38 % degradation efficiency for RhB after multiple cycles. Additionally, tetracycline (TC) was adopted as a common antibiotic to validate the versatility of the catalyst (60 mg/L, 94.06 %). The presence of oxygen vacancies and metallic Bi, ameliorated the charge separation and transfer by generating more adsorption sites and active centers, dramatically enhancing the adsorption and photocatalytic properties. Attractively, BT was innovatively explored for outdoor natural light degradation and rapid removal of RhB stained on cotton fabrics, showing the potential for practical applications. Moreover, the adsorption and photocatalytic mechanisms, possible degradation pathways of RhB and the underlying toxicity assessment of the intermediates were also elaborated. And the solution after photocatalytic treatment also exhibited considerable biocompatibility through the growth of wheat seeds and is expected to be used in agricultural field. Overall, this work opened a new avenue for the facile design of efficient adsorption-photocatalysis materials.

Degradation of multiple xanthates using highly efficient visible light-responsive BiOBr-TiO2 composite photocatalysts

BiOBr-TiO2 (BT) composite photocatalysts were synthesized by using a two-step method including hydrothermal synthesis and water-bath precipitation. The microstructural characterization analysis proved that high-crystallinity and high-purity binary BT materials were achieved without by-products. TiO2 nanoparticles with a diameter of approximately 15 nm were decorated on multi-layered BiOBr nanosheets. The results showed that BT had highly-improved adsorption capacity and photocatalytic efficiency in comparison to pristine BiOBr and TiO2. The reaction rate constant of the optimal BT-2 composite photocatalysts for the degradation of 20 mg/L sodium ethyl-xanthate could reach 0.06496 min−1, which was 2.7 and 40.3 times than pure BiOBr and TiO2, respectively. The free radical scavenger test demonstrated that photogenerated holes were the main active species in the photocatalytic degradation reaction process. A possible degradation pathway for SEX molecules was provided through the interaction of visible light and BT-2 photocatalyst. The as-prepared BT materials can be used as efficient photocatalysts to completely degrade various types of xanthates under visible light.

Natural sunlight driven photocatalytic coupling of primary amines over TiO2/BiOBr heterojunction

A natural sunlight active TiO2/BiOBr (TB) photocatalyst was prepared to efficiently utilize solar energy in green organic synthesis. Herein, the TB photocatalyst was evaluated for the oxidative coupling of benzylamine to N,N-dimethylbenzylamine at ambient temperature and pressure under natural sunlight for the first time. A high imine yield of ca. 89% is obtained from the TB heterojunction within 1 h, whereas only ca. 66% and 58% are observed from TiO2 and BiOBr, respectively. The TB also provides good to excellent yields when using benzylamine derivatives and N-heterocyclic amines, demonstrating the general applicability of the developed catalyst. Results from UV–Vis DRS, EIS, and photocurrent measurements reveal that such outstanding performance of the TB is mainly attributed to an extended light response range and an efficient charge separation and transfer efficiency derived from a type-II heterojunction configuration. Based on Hammett plot, radical scavenging results, and EPR spin trapping studies, the O2–-mediated imine formation mechanism under real solar light is then proposed. The present work not only provides insights into the amine coupling mechanisms which lay an important background for many C–N bond formation reactions but also highlights the possibility to apply this TB photocatalyst in near practical conditions.

Exceptional visible-light-induced photocatalytic activity of attapulgite–BiOBr–TiO2 nanocomposites

A novel and efficient visible-light-responsive attapulgite composite photocatalyst was fabricated by introducing BiOBr–TiO2 hybrid oxides onto its surface using in-situ depositing technique (marked as ATT–BiOBr–TiO2). ATT–BiOBr–TiO2 nanocomposites with different molar ratios of r (r=nTi/(nTi+nBi) were studied in order to achieve the best photocatalyst. The obtained samples were characterized by XRD, TEM, SEM and BET measurements. It was shown that BiOBr–TiO2 nanocomposite particles with average size of 10nm were introduced onto attapulgite fibers' surface without obvious aggregation. Compared with ATT, ATT–TiO2, ATT–BiOBr and BiOBr–TiO2, ATT–BiOBr–TiO2 exhibits exceptional visible-light photocatalytic activity in degradation of 20mg·L−1 methyl orange. The photodecomposition % of methyl orange increased along with the increasing content of TiO2 in the case of r≤0.83 and decreased as r>0.83. 96.80% of methyl orange was removed by using ATT–BiOBr–TiO2 (r=0.83) within 120min. Possible mechanism was put forward.

Advanced visible-light-driven photocatalyst BiOBr–TiO2–graphene composite with graphene as a nano-filler

As a unique 2D carbon crystal with a zero bandgap nature, superior electron mobility and high transparency, graphene was introduced into BiOBr–TiO2 (BT) composites as a nano-filler by a facile one-pot approach to obtain a novel BiOBr–TiO2–graphene (BTG) ternary photocatalyst. The material exhibits superior photocatalytic activity towards the photodegradation of Rhodamine B under visible light irradiation, and has an enhancement in photocatalytic rate of up to 2.83-fold higher than that of the BT catalyst at an optimum content of 0.75 wt% graphene in the composites. The homogeneous hybrid colloids of BiNO3, tetrabutyl titanate and graphene oxide were employed as the precursor, while GO was reduced into graphene with a simultaneous formation of tetragonal BiOBr and amorphous TiO2 in the solvothermal process. The highly dispersed 2D graphene in the composites will not only serve as the electron reservoir, but also act as a conductive network to improve the migration efficiency of electrons. Furthermore, the spacer effect of graphene will increase the surface BiOBr concentration and decrease the crystal size of BiOBr, as well as facilitate the formation of relatively uniform channel-like pores, which is beneficial for the photocatalytic performance. The photodegradation in the BiOBr–TiO2–graphene system was carried out dominantly by an indirect dye photosensitization process and the superoxide radical anions ˙O2− were considered as the main reactive species. This work provides an in-depth perspective for understanding the graphene-involved photocatalytic mechanism and stimulates the design of novel catalytic materials for the exploitation and utilization of solar energy.

Hybrid BiOBr–TiO2 nanocomposites with high visible light photocatalytic activity for water treatment

Novel highly active visible light photocatalysts BiOBr–TiO2 nanocomposites were prepared by a facile one-pot solvothermal approach. Series of characterizations verified that the BiOBr nanoscale crystals are highly dispersed in amorphous TiO2 to form the hybrid mesoporous structure. The material shows excellent photocatalytic performance towards photodegradation of Rhodamine B under visible light irradiation. The content ratio between TiO2 and BiOBr plays a key role in the microstructure of the nanocomposites, so as to result in distinguished photocatalytic activity. The sample with a molar ratio of 10 between TiO2 and BiOBr shows the optimum performance. The high photocatalytic activity of BiOBr–TiO2 nanocomposites under visible light could be ascribed to the large surface area, opened mesoporous structure, appropriate band-gap, as well as synergistic effect between TiO2 and BiOBr. Besides, the BiOBr–TiO2 composites render a facile separation due to the three-dimensional superstructure. The BiOBr–TiO2 photocatalyst is very promising for water purification as well as other environmental applications.

BiOBr–carbon nitride heterojunctions: synthesis, enhanced activity and photocatalytic mechanism

The high recombination rate of photogenerated charges is the main problem that limits the photocatalytic activity of semiconductor photocatalysts. Herein, we have reported novel heterojunctions of BiOBr–carbon nitride (BiOBr–C3N4) fabricated by depositing BiOBr nanoflakes onto the surface of C3N4. These visible light responsive heterojunctions possess intimately contacted interfaces and well-aligned straddling band-structures, which are propitious to the effective separation and transfer of photogenerated charges, bringing an improved performance. Their photocatalytic activities were evaluated by degrading Rhodamine B in aqueous solution induced by visible or indoor light. The optimum photocatalytic activity of the 0.5BiOBr–0.5C3N4 heterojunction was almost 4.9 and 17.2 times as high as those of individual BiOBr and C3N4 under visible light irradiation, and 1.5 and 48.9 times as high under indoor light irradiation, respectively. Moreover, its activity was also much higher than those of TiO2 (P25), BiOBr–TiO2, and C3N4–TiO2 heterojunctions. On the basis of experimental and theoretical results, the photocatalytic mechanism was proposed, which revealed that organic molecules were mainly oxidized by holes concentrated in the valence band of C3N4. Our work highlights that the design of heterojunctions with well-aligned straddling band-structures by combining two visible light responsive semiconductors provides an efficient method to prepare new photocatalysts working with natural light.