Emulsion-Directed Synthesis of Poly-Porphyrin Nanoparticles as Heterogeneous Photocatalysts for PET-RAFT Polymerization.

Heterogeneous photocatalysts have attracted extensive attention in photo-induced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization due to their remarkable advantages such as easy preparation, tunable photoelectric properties, and recyclability. In this study, zinc (II) 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (ZnTAPP)-based poly-porphyrin nanoparticles (PTAPP-Zn) are constructed by an emulsion-directed approach. It is investigated as a heterogeneous photocatalyst for PET-RAFT polymerization of various methacrylate monomers under visible light exposure, and the reactions show refined polymerization control with high monomer conversions. Furthermore, it is demonstrated that the PTAPP-Zn nanoparticles with the larger pore size enhance photocatalytic activity in PET-RAFT polymerization. In addition, the capabilities of oxygen tolerance and temporal control are demonstrated and PTAPP-Zn particles can be easily recycled and reused without an obvious decrease in catalytic efficiency.

Recent Advances in the Heterogeneous Photocatalytic Hydroxylation of Benzene to Phenol.

Phenol is an important chemical material that is widely used in industry. Currently, phenol is dominantly produced by the well-known three-step cumene process, which suffers from severe drawbacks. Therefore, developing a green, sustainable, and economical strategy for the production of phenol directly from benzene is urgently needed. In recent years, the photocatalytic hydroxylation of benzene to phenol, which is economically feasible and could be performed under mild conditions, has attracted more attention, and development of highly efficient photocatalyst would be a key issue in this field. In this review, we systematically introduce the recent achievements of photocatalytic hydroxylation of benzene to phenol from 2015 to mid-2022, and various heterogeneous photocatalysts are comprehensively reviewed, including semiconductors, polyoxometalates (POMs), graphitic carbon nitride (g-C3N4), metal-organic frameworks (MOFs), carbon materials, and some other types of photocatalysts. Much effort is focused on the physical and chemical approaches for modification of these photocatalysts. The challenges and future promising directions for further enhancing the catalytic performances in photocatalytic hydroxylation of benzene are discussed in the end.

Engineering Covalent Organic Frameworks as Heterogeneous Photocatalysts for Organic Transformations.

Covalent organic frameworks (COFs) are an emerging category of organic polymers with highly porous crystalline structures. In the last decade, reports on the use of COFs as heterogeneous photocatalysts for organic transformations have shown significant progress. Still, comprehensive reviews on the mechanisms of the photocatalytic organic transformations using COFs are lacking. This Review provides a comprehensive and systematic overview of COF-based photocatalysts for organic transformations. Firstly, we discuss the photophysical properties and the characterization methods of COF-based photocatalysts. Then, the general photocatalytic mechanism, the advantages, and the strategies to improve the photocatalytic efficiency of COF-based photocatalysts are summarized. After that, advanced examples of COF-based photocatalysts for organic transformations are analyzed with regard to the underlying mechanisms. The Review ends with a critical perspective on the challenges and prospects.

Influence of the Building Unit on Covalent Organic Frameworks in Mediating Photo-induced Energy-Transfer Reversible Complexation-Mediated Radical Polymerization (PET-RCMP).

Two imine-based covalent organic framework photocatalysts with different building units, TPB-DMTA-COF and TAT-DMTA-COF, for photo-induced energy transfer reversible complexation-mediated radical polymerization (PET-RCMP) were developed and investigated, producing ideal polymers with accurate molecular weight and moderate dispersity under visible light irradiation. The chain extension and spatiotemporal control experiments revealed the high chain-end fidelity of polymers and the compatibility of RCMP processes in both bulk and aqueous system. Moreover, density functional theory (DFT) calculations verified that heteroatom-doped TAT-DMTA-COF exhibits higher activities for weakening C-I bond energy barrier, which promotes PET-RCMP polymerization performance. This work demonstrates that rational adjustment of building block for constructing COF heterogeneous photocatalyst can enhance the catalytic performance of PET-RCMP, providing a design methodology for the development of polymeric organic photoelectric semiconductor catalysts to mediate RCMP.

Triazine-Carbazole-Based Covalent Organic Frameworks as Efficient Heterogeneous Photocatalysts for the Oxidation of N-aryltetrahydroisoquinolines.

Covalent organic frameworks (COFs) have attracted growing interests as new material platform for a range of applications. In this study, a triazine-carbazole-based covalent organic framework (COF-TCZ) was designed as highly porous material with conjugated donor-acceptor networks, and feasibly synthesized by the Schiff condensation of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tr ianiline (TAPB) and 9-(4-formylphenyl)-9H-carbazole-3,6-dicarbaldehyde (CZTA) under the solvothermal condition. Considering the effect of linkage, the imine-linked COF-TCZ was further oxidized to obtain an amide-linked covalent organic framework (COF-TCZ-O). The as-synthesized COFs show high crystallinity, good thermal and chemical stability, and excellent photoactive properties. Two π-conjugated triazine-carbazole-based COFs with tunable linkages are beneficial for light-harvesting capacity and charge separation efficiency, which are empolyed as photocatalysts for the oxidation reaction of N-aryltetrahydroisoquinoline. The COFs catalyst systems exhibit the outstanding photocatalytic performance with high conversion, photostability and recyclability. Photoelectrochemical tests were employed to examine the behavior of photogenerated charge carriers in photo-illumination system. The control experiments provide further insights into the nature of photocatalysis. In addition, the current research also provided a valuable approach for developing photofunctional COFs to meet challenge in achieving the great potential of COFs materials in organic conversion.

Hierarchical Bi2MoO6 microsphere photocatalysts modified with polypyrrole conjugated polymer for efficient decontamination of organic pollutants.

To effectively degrade organic pollutants in wastewater, visible-light-driven Bi2MoO6/PPy hierarchical heterogeneous photocatalysts were prepared through a solvothermal method and the following in-situ chemical oxidation polymerization. Compared with pristine Bi2MoO6 photocatalyst, the composite photocatalysts exhibited dramatically improved photocatalytic activity and photostability towards the degradation of methylene blue dye and tetracycline antibiotic. Bi2MoO6/PPy-80 sample achieved the highest photocatalytic degradation rates for methylene blue dye (93.6%) and tetracycline antibiotic (88.3%) under visible light irradiation. These two organic pollutants could be completely degraded into nontoxic small molecules according to in-depth HPLC-MS analysis of degradation products. The transient photocurrent responses, electrochemical impedance spectra, and photoluminescence spectra demonstrated that the introduction of PPy nanoparticles on the surface of Bi2MoO6 nanosheets could effectively accelerate the separation of photo-generated electron-hole pairs. Furthermore, a possible synergetic photocatalytic mechanism was put forward based on the electron spin resonance and XPS valence-band spectra. This work indicated that construction of hierarchical composite photocatalysts combining polypyrrole conductive polymer and Bi2MoO6 semiconductor in nanoscale is an efficient approach to improve photocatalytic activity for environmental remediation.

Hairy Conjugated Microporous Polymer Nanoparticles Facilitate Heterogeneous Photoredox Catalysis with Solvent-Specific Dispersibility.

Substrate accessibility is a key limiting factor for the efficiency of heterogeneous photoredox catalysis. Recently, a high photoactive surface area of conjugated microporous polymer nanoparticles (CMP NPs) has made them promising candidates for overcoming the mass transfer limitation to achieve high photocatalytic efficiency. However, this potential has not been realized due to limited dispersibility of CMP NPs in many solvents, particularly in water. Here, we report a polymer grafting strategy that furnishes versatile hairy CMP NPs with enhanced solvent-specific dispersibility. The method associates hundreds of solvent-miscible repeating units with one chain end of the photocatalyst surface, allowing minimal modification to the CMP network that preserves its photocatalytic activity. Therefore, the enhanced dispersibility of hairy CMP NPs in organic solvents or aqueous solutions affords high efficiency in various photocatalytic organic transformations.

Synthesis of zincphthalocyanine-based conjugated microporous polymers with rigid-linker as novel and green heterogeneous photocatalysts.

The novel zincphthalocyanine-based conjugated microporous polymers with rigid-linker (α-ZnPc-CMP and ß-ZnPc-CMP) were synthesized by copolymerization of zinc phthalocyanine (ZnPc) and 4, 6-diaminoresorcinol dihydrochloride (DADHC). The α-ZnPc-CMP and ß-ZnPc-CMP were utilized as heterogeneous photocatalysts to degrade Rhodamine B (RhB) in aqueous solution. It is the first time for MPc-based CMPs used as heterogeneous photocatalysts for photodegradation of RhB to date. The highly ordered skeletal alignment and two-dimensional open-channel structure of α-ZnPc-CMP and ß-ZnPc-CMP not only solve the aggregation of ZnPc and enhance its photocatalytic activity, but also facilitate the recycling and avoid the secondary pollution. The chemical structures and morphologies of α-ZnPc-CMP and ß-ZnPc-CMP were well characterized by Fourier transform infrared spectra (FT-IR), solid-state 13C nuclear magnetic resonance (13C NMR), scanning electron microscopy (SEM), N2-sorption/ desorption and X-ray diffraction (XRD). The solubility experiments and thermogravimetric analysis (TGA) showed they have good chemical stability and recyclability. Furthermore, the photocatalytic tests indicated α-ZnPc-CMP and ß-ZnPc-CMP have excellent photocatalytic performances for degradation of RhB (3 h, degraded 98 and 97.47%) in the presence of H2O2 under visible-light irradiation. All results reveal that α-ZnPc-CMP and ß-ZnPc-CMP have great potential as photocatalysts on the degradation of organic dye contaminants. Moreover, the possible reaction mechanism of α-ZnPc-CMP and ß-ZnPc-CMP as photocatalysts for the degradation of RhB is proposed.

Graphene-Based Nanocomposites for Efficient Photocatalytic Hydrogen Evolution: Insight into the Interface toward Separation of Photogenerated Charges.

Although the reduced graphene oxide (rGO) has been intensively applied for photocatalytic H2 evolution, no enough attention was given to study the interface between the photocatalyst and rGO, which is the key point to affect the transportation of the photogenerated electron. Herein, in order to research the heterojunction interface, a series of SrTiO3 photocatalysts with different crystal facets were fabricated to be loaded with the rGO for photocatalytic H2 evolution. The characterizations and theory calculation verified that the rGO was mainly anchored on the Ti-O bond of the SrTiO3 in the composite. Therefore, compared to the {001} facets sample, the {110} facets of the SrTiO3, which exposed more Ti and O atoms, could form a stronger bond with the rGO. Additionally, the density functional theory study deduced that the photoinduced electron could immigrate rapidly from the Ti-O bond to the rGO in the composite, which was in good agreement with the results of photoelectrochemical and photoluminescence experiments. Meanwhile, experimentally, the 1% wt rGO@SrTiO3 with {110} facets nanocomposite showed the superior photocatalytic H2 yield rate (3.82 mmol/h/g), which was 2.2 times and 3.2 times higher than that of the pure SrTiO3 with the same facets and 1% wt rGO@SrTiO3 with {001} facets, respectively. Both experiments and theoretical calculations unveiled that the synergetic effect of SrTiO3 facets engineering and the rGO loading effectively prompted the immigration of photoinduced electrons at the nanocomposite interface. This work provides a rational thinking of a high efficiency rGO-based heterogeneous photocatalysts for solar energy conversion.