Separation Of Photogenerated Charge Carriers Research Articles

Tetragonal/orthorhombic-bismuth tungstate homojunction formed through in situ bismuth induced phase transformation as highly efficient photocatalyst for pollutant degradation

Tetragonal/orthorhombic-bismuth tungstate (t/o-Bi2WO6) homojunctions of high photocatalytic efficiencies were fabricated through a novel in situ Bi induced phase transformation. The photocatalytic efficiencies of t-Bi2WO6 were greatly enhanced via formation of the homojunction. Photocatalytic degradation of rhodamine B (RhB), a recalcitrant organic pollutant, under simulated sunlight illumination was investigated as a demonstration for the efficiency enhancement. A 6.22 folds improvement was achieved with formation of the homojunction in terms of reaction rate constants. The homojunction catalyst was demonstrated to be photocatalytically stable over a five cycles operation. The t/o-Bi2WO6 homojunction enhances separation and utilization efficiency of photo-generated charge carriers and thus greatly boosts the catalytic efficiency. Trapping tests and electron spin resonance spectroscopy were conducted to reveal that singlet oxygen (1O2), hole (h+), electrons (e−), and superoxide anion radical (O2−) are the main working reactive species for RhB degradation. Density functional theory (DFT) calculations were performed to prove the feasibility of Bi induced phase transformation of t-Bi2WO6 to o-Bi2WO6. The present development offers a new design route for high efficiency photocatalysts for water pollution control.

Hybridization of Schiff base network and amino functionalized Cu based MOF to enhance photocatalytic performance

In this work, an amine-functionalized Cu-based metal-organic framework (MOF) was prepared through the solvothermal method. The synthesized Cu- MOF was hybridized with Schiff base network-1 (SNW-1), as a new production of covalent organic frameworks (COFs). In order to use the synthesized nanohybrid as a photocatalyst in the visible light region, the structure of the photocatalyst was modified by adding cadmium sulfide (CdS). The lab synthesized CdS/SNW-1/Cu-MOF nanohybrid photocatalyst was evaluated for cationic (Basic Red 46 (BR46)) and anionic (Congo red (CR)) dyes-waste treatment under visible light. The as-prepared samples were characterized by various techniques. Cu-MOF, SNW-1, and CdS nanoparticles have cubic, spherical and hexagonal shapes in CdS/Cu-MOF/SNW-1 nanohybrid, respectively. The above results show that the synergistic effect existing between CdS, SNW-1, and Cu-MOF leads to efficient photogenerated charge carriers separation and consequently improves contaminants' photo-removal treatment of the nanohybrid. The enhanced surface area, the improved structure crystallinity, the amended uniformity of pores distribution, the boosted visible light harvesting, the efficient charge transfer/separation, along the suppressed recombination of photogenerated electron-hole pairs are significant factors in the photo-removal advanced rates of the synthesized substrate.

The impact of benzene ring embedding on the performance of carbon nitride for photocatalytic hydrogen

Forming local micro-π conjugate connection units in the structure of carbon nitride (CN) at the interface to capture photo-generated electrons can reduce the band gap and simultaneously facilitate the charge transfer. Herein, the H3BTC/CN composites with benzene ring embedded structure were prepared through the acid-base reaction between H3BTC and melamine. The precursor reaction method effectively enhanced the dispersity and utilization efficiency of modification molecule. The introduced benzene ring of H3BTC increased the double bonds of π conjugated system, decreased the band gap and widened the response range of visible light. At the same time, benzene ring acted as the electron acceptor to capture photo-generated electrons and promote the effective separation of photo-generated charge carriers. The optimal catalyst, 7.5 wt% H3BTC/CN showed an enhanced photocatalytic hydrogen evolution rate of 301 μmol g-1h−1, which was 21.8 times higher than that of pure CN. The work manifested the positive impact of benzene ring embedding on CN structure and photocatalytic performance, which proposed a new strategy for the design and preparation of high-efficiency photocatalyst.

Morphology Engineering of BiVO4 with CoOx Derived from Cobalt-containing Polyoxometalate as Co-catalyst for Oxygen Evolution.

Bismuth vanadate (BiVO4 ) as a metal oxidation semiconductor has stimulated extensive attention in the photocatalytic water splitting field. However, the poor transport ability and easy recombination of charge carriers limit photocatalytic water oxidation activity of pure BiVO4 . Herein, the photocatalytic activity of BiVO4 is enhanced via adjusting its morphology and combination co-catalyst. First, the Cu-BiVO4 was synthesized by copper doping to control the growth of {110} facet of BiVO4 , which is regarded for the separation of photo-generated charge carriers. Then the CoOx in-situ generated from K6 [SiCoII (H2 O)W11 O39 ] ⋅ 16H2 O was photo-deposited on Cu-BiVO4 surface as co-catalyst to speed up reaction kinetics. Cu-BiVO4 @CoOx hybrid catalyst shows highest photocatalytic activity and best stability among all the prepared catalysts. Oxygen evolution is about 34.6 μmol in pH 4 acetic acid buffer under 420 nm LED irradiation, which is nearly 20 times higher than that of pure BiVO4 . Apparent quantum efficiency (AQE) in 1 h and O2 yield are 1.83% and 23.1%, respectively. O2 evolution amount nearly maintains the original value even after 5 cycles.

Visible Light Photocatalytic Degradation of Sunset Yellow Dye and Industrial Textile Wastewater Using Pd-BiFeO3 Composite

Herein, pristine BiFeO3 and Pd-incorporated BiFeO3 (Pd-BiFeO3) composite were synthesized using hydrothermal synthesis method. The physiochemical and optical properties of the synthesized materials were investigated using numerous techniques. The Pd-BiFeO3 composite significantly enhanced the photocatalytic degradation of sunset yellow (SSY) dye in comparison with the pristine BiFeO3 under visible light irradiation. The enhanced photoactivity was credited to the improved photogenerated charge carrier separation, which was in accordance with the photoelectrochemical measurements. Moreover, the Pd-BiFeO3 composite can be recycled for seven consecutive runs without sufficient loss of photocatalytic activity. Radical trapping studies suggested that the hydroxyl radical (•OH), hydrogen peroxide (H2O2) and hole (h+) were the key reactive oxidizing species. A possible photocatalytic enhancement mechanism of Pd-BiFeO3 composite was stated. Finally, for the first time, the Pd-BiFeO3 composite was also applied towards the effective degradation of industrial textile wastewater.

Facile construction of dual heterojunction CoO@TiO2/MXene hybrid with efficient and stable catalytic activity for phenol degradation with peroxymonosulfate under visible light irradiation

Photocatalysis and peroxymonosulfate (PMS) based advanced oxidation processes (AOP) are emerging technology for the degradation of refractory organic pollutant in the field of water treatment. Here we report a novel CoO@TiO2/MXene (CTM) hybrid through a facile sonication-hydrothermal method for efficient degradation of phenol via an integrated PMS activation-photocatalysis process. Benefiting from the proper position and superior suitability of the band structure, a dual interfacial charge transport channel was constructed, boosting the separation of photo-generated charge carriers and generating sufficient potential difference for redox reaction. Accordingly, the CTM hybrid not only possessed the outstanding photocatalytic activity but also dramatically accelerated PMS activation to generate considerable reactive radicals. As a result, over 96% phenol degradation was achieved in the 10% CTM/PMS/Vis system within 15 min. The radical quenching test and EPR analysis reveal that SO4•−, O2•− and 1O2 were predominant reactive species involved in the catalytic process. Moreover, the damaged chemical structure of CoO during PMS activation could be healed by the photo-actuated Co(II) regeneration to allow for continuous and stable catalytic process. This study offers a promising perspective for the rational design of competent and stable hybrid heterojunction catalyst to construct PMS activation-photocatalysis processes for the efficient degradation of organic contaminants.

In-situ preparation of TiO2/N-doped graphene hollow sphere photocatalyst with enhanced photocatalytic CO2 reduction performance

Photocatalytic CO2 conversion efficiency is hampered by the rapid recombination of photogenerated charge carriers. It is effective to suppress the recombination by constructing cocatalysts on photocatalysts with high-quality interfacial contact. Herein, we develop a novel strategy to in-situ grow ultrathin N-doped graphene (NG) layer on TiO2 hollow spheres (HS) with large area and intimate interfacial contact via a chemical vapor deposition (CVD). The optimized TiO2/NG HS nanocomposite achieves total CO2 conversion rates (the sum yield of CO, CH3OH and CH4) of 18.11 μmol g−1 h−1, which is about 4.6 times higher than blank TiO2 HS. Experimental results demonstrate that intimate interfacial contact and abundant pyridinic N sites can effectively facilitate photogenerated charge carrier separation and transport, realizing enhanced photocatalytic CO2 reduction performance. In addition, this work provides an effective strategy for in-situ construction of graphene-based photocatalysts for highly efficient photocatalytic CO2 conversion.

Enhanced Photocatalytic Degradation of Perfluorooctanoic Acid by Mesoporous Sb2O3/TiO2 Heterojunctions.

Perfluorooctanoic acid (PFOA), a typical perfluorinated carboxylic acid, is an emerging type of permanent organic pollutants that are regulated by the Stockholm Convention. The degradation of PFOA, however, is quite challenging largely due to the ultra-high stability of C-F bonds. Compared with other techniques, photocatalytic degradation offers the potential advantages of simple operation under mild conditions as well as exceptional decomposition and defluorination efficiency. Titanium dioxide (TiO2) is one of the most frequently used photocatalysts, but so far, the pristine nanosized TiO2 (e.g., the commercial P25) has been considered inefficient for PFOA degradation, since the photo-generated hydroxyl radicals from TiO2 are not able to directly attack C-F bonds. Mesoporous Sb2O3/TiO2 heterojunctions were therefore rationally designed in this work, of which the confined Sb2O3 nanoparticles in mesoporous TiO2 framework could not only tune the band structure and also increase the number of active sites for PFOA degradation. It was found that, after loading Sb2O3, the absorption of UV light was enhanced, indicating a higher efficiency of light utilization; while the band gap was reduced, which accelerated the separation of photo-generated charge carriers; and most importantly, the valence band edge of the Sb2O3/TiO2 heterojunction was significantly lifted so as to prevent the occurrence of hydroxyl radical pathway. Under the optimal ratio of Sb2O3–TiO2, the resulting catalysts managed to remove 81.7% PFOA in 2 h, with a degradation kinetics 4.2 times faster than the commercial P25. Scavenger tests and electron spin resonance spectra further revealed that such improvement was mainly attributed to the formation of superoxide radicals and photo-generated holes, in which the former drove the decarboxylation from C7F15COOH–C7F15 •, and the latter promoted the direct electron transfer for the conversion of C7F15COO−–C7F15COO•. The Sb2O3/TiO2 photocatalysts were highly recyclable, with nearly 90% of the initial activity being retained after five consecutive cycles, guaranteeing the feasibility of long-term operation.

Constructing CdSe QDs modified porous g-C3N4 heterostructures for visible light photocatalytic hydrogen production

Constructing heterostructures with narrow-band-gap semiconductors is a promising strategy to extend light absorption range of graphitic carbon nitride (g-C3N4) and simultaneously promote charge separation for its photocatalytic activity improvement. However, its highly localized electronic states of g-C3N4 hinder photo-carrier migration through bulk towards heterostructure interfaces, resulting in low charge carrier separation efficiency of solid bulk g-C3N4-based heterostructures. Herein, porous g-C3N4 (PCN) material with greatly shortened migration distance of photo-carriers from bulk to surface was used as an effective substrate to host CdSe quantum dots to construct type II heterostructure of CdSe/PCN for photocatalytic hydrogen production. The homogeneous modification of the CdSe quantum dots throughout the whole bulk of PCN together with proper band alignments between CdSe and PCN enables the effective separation of photo-generated charge carriers in the heterostructure. Consequently, the CdSe/PCN heterostructure photocatalyst gives the greatly enhanced photocatalytic hydrogen production activity of 192.3 μmol h−1, which is 4.4 and 8.1 times that of CdSe and PCN, respectively. This work provides a feasible strategy to construct carbon nitride-based heterostructure photocatalysts for boosting visible light driven water splitting performance.

Synergistic Effect of Co/La in Oxygen Vacancy Rich Ternary CoAlLa Layered Double Hydroxide with Enhanced Reductive Sites for Selective Photoreduction of CO2 to CH4

Developing a convenient ternary layered double hydroxide (LDH) semiconductor for highly active photocatalytic reduction is necessary for solving the energy crisis and environmental pollution. In this work, a highly active ternary CoAlLa-LDH was formed through inducing La³⁺ to enhance coordinatively unsaturated metals centers for development of reductive sites that resulted in improvement of photogenerated charge carrier separation. It was demonstrated that the ratio of cations between the Co/Al/La-LDHs greatly determined the LDH structure for photocatalytic activity toward CO₂ reduction. The increase of La content resulted in destruction of LDH structure with lower photoactivity for CO₂ reduction. The rate of CO and CH₄ evolution in Co₂Al₁-LDH was about 15.3 and 9.2 μmol gcₐₜ–¹ h–¹, much higher than Co₃Al₁-LDH and Co₄Al₁-LDH, which indicates that the Co₂Al₁-LDH among CoAl-LDHs is a promising photocatalyst with high photocatalytic activity in CO₂ reduction to CO and CH₄. The Co/Al/La molar ratios were optimized to be 2:0.95:0.05 with a production rate of 25.5 μmol gcₐₜ–¹ h–¹ and 21.80 μmol gcₐₜ–¹ h–¹ for CH₄ and CO, respectively. A more interesting finding is that the selectivity of CH₄ was raised to 53.93% as compared to 46.10% for CO. Besides, good stability was observed due to the presence of the intact hexagonal nanosheet structure, which was sustained in multiple cycles without obvious deactivation. The highest activity was due to the proper weaving of lanthanum into the framework of LDH. This work demonstrates a facile synthetic method of rationally doping La transition-metal to develop new photocatalyst with remarkable performance in CO₂ reduction.

Significantly influenced photocatalytic performance for H2O2 generation over ultrathin g-C3N4 through regulating the migration orientation of photogenerated charge carriers

H2O2 has been widely applied in the fields of chemical synthesis, medical sterilization, pollutant removal, etc., due to its strong oxidizing property and the avoidable secondary pollution. Despite of the enhanced performance for H2O2 generation over g-C3N4 semiconductors through promoting the separation of photo-generated charge carriers, the effect of migration orientation of charge carriers is still ambiguous. For this emotion, surface modification of g-C3N4 was employed to adjust the migration orientation of charge carriers, in order to investigate systematically its effect on the performance of H2O2 generation. It was found that ultrathin g-C3N4 (UCN) modified by boron nitride (BN), as an effective hole-attract agent, demonstrated a significantly enhanced performance. Particularly, for the optimum UCN/BN-40% catalyst, 4.0-fold higher yield of H2O2 was obtained in comparison with the pristine UCN. As comparison, UCN modified by carbon dust demonstrated a completely opposite tendency. The remarkably improved performance over UCN/BN was ascribed to the fact that more photo-generated electrons were remained inside of triazine structure of g-C3N4, leading to the formation of larger amount of 1,4-endoxide. It is anticipated that our work could provide new insights for the design of photocatalyst with significantly improved performance for H2O2 generation.

Structural, electrical, and photocatalytic investigations of PANI/ZnO nanocomposites

In recent days, conducting polymers with inorganic metal oxide has provoked a great deal of interest towards electrochemical and photocatalytic applications. In this regard, the organic-inorganic polyaniline (PANI)/ZnO nanocomposite with different weight percentages (1 and 10) of ZnO in the PANI matrix was synthesized through in situ polymerization approach. The structural, optical, electrical, and photocatalytic properties of the synthesized PANI/ZnO nanocomposites were systematically studied. Interestingly, PANI/ZnO (10 wt%) composition possesses excellent conductivity behavior (ρ = 4.35 × 10−3 S cm−1) and displayed maximum photocatalytic activity of K = 14.77 × 10−3 min−1 for the degradation of methylene blue (MB) in aqueous solution (10 ppm) under natural sunlight. The superiority of both the conductivity and photocatalytic efficiencies of PANI/ZnO (10 wt%) nanocomposites might be due to synergistic interaction between PANI and ZnO and high photogenerated charge carrier separation.

Tuning the Electronic Bandgap of Graphdiyne by H‐Substitution to Promote Interfacial Charge Carrier Separation for Enhanced Photocatalytic Hydrogen Production

AbstractGraphdiyne (GDY), which features a highly π‐conjugated structure, direct bandgap, and high charge carrier mobility, presents the major requirements for photocatalysis. Up to now, all photocatalytic studies are performed without paying too much attention on the GDY bandgap (1.1 eV at the G0W0 many‐body theory level). Such a narrow bandgap is not suitable for the band alignment between GDY and other semiconductors, making it difficult to achieve efficient photogenerated charge carrier separation. Herein, for the first time, it is demonstrated that tuning the electronic bandgap of GDY via H‐substitution (H‐GDY) promotes interfacial charge separation and improves photocatalytic H2 evolution. The H‐GDY exhibits an increased bandgap energy (≈2.5 eV) and exploitable conduction band minimum and valence band maximum edges. As a representative semiconductor, TiO2 is hybridized with both H‐GDY and GDY to fabricate a heterojunction. Compared to the GDY/TiO2, the H‐GDY/TiO2 heterojunction leads to a remarkable enhancement of the photocatalytic H2 generation by 1.35 times under UV–visible illumination (6200 µmol h−1 g−1) and four times under visible light (670 µmol h−1 g−1). Such enhancement is attributed to the suitable band alignment between H‐GDY and TiO2, which efficiently promotes the photogenerated electron and hole separation, as supported by density functional theory calculations.

Covalent organic framework stabilized CdS nanoparticles as efficient visible-light-driven photocatalysts for selective oxidation of aromatic alcohols

Noble-metal-free photocatalysts with high and stable performance provide an environmentally-friendly and cost-efficient route for green organic synthesis. In this work, CdS nanoparticles with small particle size and different amount were successfully deposited on the surface of covalent organic frameworks (COFs). The deposition of suitable content of CdS on COFs could not only modify the light adsorption ability and the intrinsic electronic properties, but also enhance the photocatalytic activity and cycling performance of CdS for the selective oxidation of aromatic alcohols under visible light. Especially, COF/CdS-3 exhibited the highest yield (97.1%) of benzaldehyde which is approximately 2.5 and 15.9 times as that of parental CdS and COF, respectively. The results show that the combination of CdS and COF can improve the utilization of visible light and the separation of photo-generated charge carriers, and COF with the π-conjugated system as supports for CdS nanoparticles could provide efficient electron transport channels and improve the photocatalytic performance. Therefore, this kind of COF-supported photocatalysts with accelerated photo-induced electrons and charge-carrier separation between semiconductors possesses great potentials in future green organic synthesis.

In situ growth of 1D/2D CdS–Bi2MoO6 core shell heterostructures for synergistic enhancement of photocatalytic performance under visible light

Stability of the photocatalyst, maximum solar energy harvesting and effective photogenerated charge carrier separation are yet demanding key features of the photocatalysis for pollutant abetment and photo-electrochemical applications. Herein, we report the in situ solvothermal synthesis of CdS–Bi2MoO6 core-shell heterostructures (CdS–Bi2MoO6 CSHs) for the photocatalytic elimination of methyl orange (MO) under visible light. The as-synthesized CdS–Bi2MoO6 CSHs exhibited highest photocatalytic performance of 98.5%, which is approximately 10 and 4 folds higher than pristine Bi2MoO6 nanosheets (NSs) and CdS nanorods (NRs), respectively. This significantly enhanced photocatalytic performance is attributed to the core-shell heterostructure that improves the visible-light harvesting ability, facilitates efficient separation and transfer of the photogenerated charge carriers, as well as synergistic band alignment of both CdS NRs and Bi2MoO6 NSs. The CdS–Bi2MoO6 CSHs also showed efficient photocatalytic performance toward methylene blue (MB) as colored dye and tetracycline hydrochloride (TCH) as a colorless emerging contaminant. Additionally, the outcomes of transient photocurrent, electrochemical impedance, and photoluminescence study further corroborate that the construction of core-shell heterostructures with tight contact, leading to effective charge carrier separation. The hole (h+) and superoxide radical anion (•O2−) were determined to be the predominant active species accountable for the MO dye degradation. Furthermore, the CdS–Bi2MoO6 CSHs exhibited a satisfactory recycling efficiency over five cycles (reduced by approximately 6%), owing to the protective Bi2MoO6 NSs shell over the CdS NRs core, demonstrating their applicability in wastewater purification and photo-electrochemical applications.

NiS/Pt nanoparticles co-decorated black mesoporous TiO2 hollow nanotube assemblies as efficient hydrogen evolution photocatalysts

A novel mesoporous Pt/NiS/black TiO2 hollow nanotubes (P-NBTNs) is assembled by a facile synthesize route based on hollow black TiO2 nanotubes with 2D mesoporous TiO2 nanosheets. This unique structure increases the specific surface area of the material, exposes more photocatalytic reaction active sites, and reduces the bandgap to about 2.87 eV, thereby improving its light absorption capacity in the visible light region. At the same time, the surface plasmon resonance effect of the noble metal Pt is employed to further improve the absorption and utilization of visible light. The strong electron-withdrawing ability of Pt nanoparticles and the synergistic catalytic between NiS and Pt, and the formation of built-in electric field at the interface all promote the separation and transmission of photo-generated charge carriers, leading to significant improvement of photocatalytic performance. Under AM 1.5 G irradiation, the hydrogen production rate of P-NBTNs is up to 4.70 mmol h−1g−1, which is more than 4 times higher than that of pristine TiO2 nanotubes (TNs) (~0.94 mmol h−1g−1). The photocatalytic performance nearly keeps constant after more than 10 cycles, indicating the high stability of P-NBTNs, which favors the practical applications.

First-principles investigation on the interfacial interaction and electronic structure of BiVO4/WO3 heterostructure semiconductor material

The BiVO4/WO3 heterostructure material is promising photoanode architecture in photoelectrocatalysis hydrogen generation system. However, most studies focused on the relationship between BiVO4/WO3 heterostructure material preparation method, morphology design, heteroatom doping and efficiency. Its internal mechanism and interface engineering have not been investigated in theory. In this work, these questions are answered by exploring the structure, electronic and optical properties of the system, as well as investigating the band arrangement and charge transfer when the interfacial interaction goes from van der Waals form to binding form. The binding form occurs when WO3 slab and BiVO4 slab are close enough to form a coherent boundary. It is found that the combination of WO3 and BiVO4 can form a heterostructure of type-II energy band arrangement and the formation of built-in electric field at the interface, which allows for better photogenerated charge carrier separation. When the interface binding form appears, the interface channel effect makes the maximum effective electron accumulation more than 4 times that of van der Waals form. Our work not only provides a perspicacious understanding of the photoexcited carrier separation mechanism for BiVO4/WO3 heterostructure, but also sheds light on exploring interfacial interaction in other heterostructure semiconductor materials.

Modulating oxygen vacancies on bismuth-molybdate hierarchical hollow microspheres for photocatalytic selective alcohol oxidation with hydrogen peroxide production

Photocatalytic selective oxidation of alcohols into high value-added carbonyl compounds accompanied by producing hydrogen peroxide (H2O2) is undoubtedly a more efficient solar energy conversion strategy with high atom economy. Herein, we have developed an efficient photocatalyst of bismuth-molybdate (Bi2MoO6) hierarchical hollow microspheres with tunable surface oxygen vacancies (OVs) for promoting the photocatalytic selective alcohol oxidation with H2O2 production. The effect of surface OVs on the photocatalytic efficiency is studied systematically by comparing the performance of different photocatalysts. The benzaldehyde and H2O2 production rates over the OV-rich Bi2MoO6 photocatalyst reach up to 1310 and 67.2 μmol g−1 h−1, respectively, which are 2.3 and 4.0 times those generated from the OV-poor Bi2MoO6 hollow microspheres. The roles of various active radicals in the photocatalytic reaction are probed by a series of controlled experiments and in situ ESR measurements, revealing that both superoxide radical (•O2-) and carbon-centered radical are the key active intermediates. The introduction of surface OVs on Bi2MoO6 hollow microspheres accelerates the separation and transfer of photo-generated charge carriers as well as enhances the adsorption and activation of reactant molecules, thereby greatly promoting the photocatalytic selective oxidation of alcohols along with H2O2 production. This work not only demonstrates a facile strategy for the preparation of high-efficiency photocatalysts by simultaneous modulations of morphology and surface defects, but also offers insight into developing the dual-functional photocatalytic reactions for the full utilizations of photoinduced electrons and holes.

Synthesis of g-C3N4/W-SBA-15 Composites for Photocatalytic Degradation of Tetracycline Hydrochloride

Graphitic carbon nitride (g-C3N4) and tungsten incorporated SBA-15 (W-SBA-15) hybrid materials were prepared by a facial thermal polymerization method using dicyandiamide as a precursor and W-SBA-15 as a support. The as-prepared samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (UV–Vis DRS). The catalytic properties of g-C3N4/W-SBA-15 composites were assessed by degrading tetracycline hydrochloride (TC) under simulated solar light irradiation. Results from characterizations revealed that the addition of g-C3N4 to W-SBA-15 could apparently improve the photocatalytic degradation properties. Among these catalysts, g-C3N4(3.0)/W-SBA-15 exhibited the highest catalytic activity, which was almost 4.3 times greater than that of W-SBA-15. The enhanced photocatalytic activity of g-C3N4/W-SBA-15 may be due to the formation of heterojunction between g-C3N4 and tungsten species, resulting in the effective separation of photo-generated charge carriers and increased absorption of visible light. Moreover, the g-C3N4/W-SBA-15 composite had high cycling reusability and stability, which was an important factor for its potential actual applications.

In situ synthesis of “brick and mortar”-type lignin-derived carbon/TiO2 composite with a remarkable photocatalytic performance

Alkali lignin (AL), an industrial waste from pulping black liquor, is mainly applied as a low-grade combustible energy source. Design and preparation of high value-added materials with AL is still a challenge. In this work, we firstly introduced ammonium group into AL and prepared quaternized alkali lignin (QAL) for improving the solubility in acidic aqueous solution. Then a facile sol–gel and carbonization process was developed to fabricate lignin-derived carbon/TiO2 (LC/TiO2) composite photocatalyst using QAL as the carbon precursor. The microstructural characteristics and optical property of the LC/TiO2 composite were systematically characterized. Composite exhibited a “brick (TiO2 nanoparticles) and mortar (LC)”-type construction, and TiO2 nanoparticles were coated with LC. The introduction of LC endowed TiO2 with extended photoabsorption region and enhanced separation of photo-generated charge carriers. LC/TiO2 obtained at a carbonization temperature of 650°C presented the highest photocatalytic activity for the degradation of organic dye, which was about 3.4 times that of bare TiO2. Moreover, LC/TiO2 also presented good recyclability. This facile strategy not only offers great opportunities for the high value-added application of industrial lignin, but also promotes the practical application of TiO2 photocatalyst.