Porphyrin-Based Nanomaterials for the Photocatalytic Remediation of Wastewater: Recent Advances and Perspectives

[Ru(bpy)3]2+ Derivatives-Incorporated POM@MOFs with Good Photocatalytic Activity for Visible-Light-Driven Oxidative Coupling of Amines to Imines

Two novel POM@MOFs, {H3Zn2.5(H2O)10[Ru(dcbpy)3][PMo11VIMoVO40]}·2H2O (RuZn-PMo) and {H3Ni2.5(H2O)12[Ru(dcbpy)3][PMo11VIMoVO40]}·5H2O (RuNi-PMo), have been synthesized through a traditional hydrothermal method. They are composed of [Ru(bpy)3]2+-derived hexa-carboxylate and Keggin-type anion [PMo11VIMoVO40]4-. In addition, their structures were well characterized by various spectroscopic methods. Under the irradiation of visible light (λ > 400 nm), RuZn-PMo and RuNi-PMo as heterogeneous photocatalysts showed efficient photocatalytic performance in the coupling reaction of amines, with TONs of 451 and 454, respectively. Moreover, RuZn-PMo exhibited excellent reusability and stability after three continuous reaction cycles. Besides, EPR measurements were performed to elucidate the reaction mechanism.

Photocatalytic Recovery of Noble Metals by Covalent Silyl Polyoxophosphotungstate-Porphyrin Copolymers

The photocatalytic recovery of noble metals on photosensitive semiconductors such as TiO2 is well-established for forming M/TiO2 but has notable drawbacks. TiO2 suffers from low conversion efficiency due to significant recombination of photogenerated electron-hole pairs. Its wide energy band gap (3.2 eV) also restricts excitation to high-energy UV light, limiting its use with solar energy. This study proposes an efficient alternative using hybrid polyoxometalate (POM)-porphyrin copolymers for the photocatalytic recovery of Ag and Pt under visible light. Copolymeric films composed of hybrid polyoxometalates and porphyrins have been obtained by the electrooxidation of 5,15-(di-p-tolyl)porphyrin (H2T2P) or 2,3,7,8,12,13,17,18-octaethylporphine zinc(II) (ZnOEP) together with Keggin or Wells-Dawson-type organosilyl polyoxophosphotungstate ([PW11Si2O40C26H16N2]TBA3 or [P2W17Si2O62C26H16N2]TBA6). In these films, porphyrin subunits can be excited under visible illumination, acting as photosensitizers that transfer electrons to the polyoxometalate catalysts. Notably, POM-porphyrin films demonstrated high efficiency in Pt(IV) photoreduction over repeated cycles without catalyst degradation.

Near-Perfect Purification of 2,6-Xylenol from Ternary Cresol Mixtures Using Cucurbit[7]uril

The separation of m-cresol (m-cre), p-cresol (p-cre), and 2,6-xylenol (2,6-xyl) poses a significant challenge in industrial processes. This study focuses on selectively separating m-cre and p-cre from a ternary mixture using a cucurbit[7]uril (Q[7]) aqueous solution to achieve the near-perfect purification of 2,6-xyl. Experimental results show that m-cre and p-cre can be selectively encapsulated by the Q[7] host, while 2,6-xyl, due to its larger volume, cannot be encapsulated. The synergistic effect of steric hindrance and complex stability contributes to effective host-guest selective encapsulation separation. The Q[7] aqueous solution can be easily recovered and reused without a significant decrease in separation performance. In the simulated industrial separation experiment, the purity of the purified cresol reached 100%. This research underscores the importance of macrocyclic host molecules in enhancing industrial separations and reducing energy costs through precise guest molecule recognition.

Two-dimensional porous porphyrin materials composed of robust tin(IV)-porphyrin linkages for photocatalytic wastewater remediation

Porphyrin-based two-dimensional porous materials (SnP-H2TCPP, SnP-ZnTCPP) composed of robust Sn(IV)-porphyrin linkages have been synthesized by reacting trans-dihydroxo[5,10,15,20-tetraphenylporphyrinato]tin(IV) (SnP) with [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin] (H2TCPP) and [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato]zinc(II) (ZnTCPP), respectively. The strength of the interaction between the carboxylic acid group of the monomeric porphyrins (H2TCPP and ZnTCPP) and the axial hydroxyl moiety of SnP enables the construction of highly stable framework materials, which were characterized by FT-IR, UV-vis, and emmission spectroscopy, powder XRD, elemental analysis, and thermogravimetric analysis (TGA). SnP-H2TCPP and SnP-ZnTCPP absorb visible light strongly over a wide range, demonstrating weak perturbation in the electronic ground state structures of the π-conjugated aromatic moieties compared to the starting monomeric units. TGA indicated that SnP-H2TCPP and SnP-ZnTCPP exhibited greater thermal stability than SnP. The permanent porosity of SnP-H2TCPP and SnP-ZnTCPP resulted in large specific surface areas (BET) of 210.0 m2 g-1 and 185.0 m2 g-1, respectively. Uniform spherical nanoplates with an average diameter in the range of 900-1000 nm were observed for SnP-H2TCPP, whereas a nanocomposite morphology was observed for SnP-ZnTCPP, whose shape and size could not be specifically defined. Finally, the photodegradation performance of SnP-H2TCPP and SnP-ZnTCPP was found to be 89% (K = 0.0179 min-1) and 97% (K = 0.0246 min-1) within 120 min, respectively, for the degradation of methylene blue (MB), and 50% (K = 0.0091 min-1) and 60% (K = 0.0120 min-1) within 75 min, respectively, for the tetracycline (TC) antibiotic. The enhanced catalytic photodegradation activity of SnP-H2TCPP or SnP-ZnTCPP is attributed to the cooperation between the carboxylate-bearing porphyrin units and SnP.

Tin(IV)Porphyrin-Based Porous Coordination Polymers as Efficient Visible Light Photocatalyst for Wastewater Remediation

Two porphyrin-based polymeric frameworks, SnP-BTC and SnP-BTB, as visible light photocatalysts for wastewater remediation were prepared by the solvothermal reaction of trans-dihydroxo-[5,15,10,20-tetrakis(phenyl)porphyrinato]tin(IV) (SnP) with 1,3,5-benzenetricarboxylic acid (H3BTC) and 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB), respectively. The strong bond between the carboxylic acid group of H3BTC and H3BTB with the axial hydroxyl moiety of SnP leads to the formation of highly stable polymeric architectures. Incorporating the carboxylic acid group onto the surface of SnP changes the conformational frameworks as well as produces rigid structural transformation that includes permanent porosity, good thermodynamic stability, interesting morphology, and excellent photocatalytic degradation activity against AM dye and TC antibiotic under visible light irradiation. The photocatalytic degradation activities of AM dye were found to be 95% by SnP-BTB and 87% by SnP-BTC within 80 min. Within 60 min of visible light exposure, the photocatalytic degradation activities of TC antibiotic were found to be 70% by SnP-BTB and 60% by SnP-BTC. The enhanced catalytic photodegradation performances of SnP-BTB and SnP-BTC were attributed to the synergistic effect between SnP and carboxylic acid groups. The carboxylic acid connectors strongly resist the separation of SnP from the surface of SnP-BTB and SnP-BTC during the photodegradation experiments. Therefore, the high degradation rate and low catalyst loading make SnP-BTB or SnP-BTC more efficient than other reported catalysts. Thus, the present investigations on the porphyrin-based photocatalysts hold great promise in tackling the treatment of dyeing wastewater.

Nanolabels Prepared by the Entrapment or Self-Assembly of Signaling Molecules for Colorimetric and Fluorescent Immunoassays

Nanomaterials have attracted significant attention as signal reporters for immunoassays. They can directly generate detectable signals or release a large number of signaling elements for readout. Among various nanolabels, nanomaterials composed of multiple signaling molecules have shown great potential in immunoassays. Generally, signaling molecules can be entrapped in nanocontainers or self-assemble into nanostructures for signal amplification. In this review, we summarize the advances of signaling molecules-entrapped or assembled nanomaterials for colorimetric and fluorescence immunoassays. The nanocontainers cover liposomes, polymers, mesoporous silica, metal-organic frameworks (MOFs), various nanosheets, nanoflowers or nanocages, etc. Signaling molecules mainly refer to visible and/or fluorescent organic dyes. The design and application of immunoassays are emphasized from the perspective of nanocontainers, analytes, and analytical performances. In addition, the future challenges and research trends for the preparation of signaling molecules-entrapped or assembled nanolabels are briefly discussed.

Self-Assembled Nanostructure of Ionic Sn(IV)porphyrin Complex Based on Multivalent Interactions for Photocatalytic Degradation of Water Contaminants

[Sn(H2PO4)2(TPyHP)](H2PO4)4∙6H2O (2), an ionic tin porphyrin complex, was synthesized from the reaction of [Sn(OH)2TPyP] (1) with a dilute aqueous solution of a polyprotic acid (H3PO4). Complex 2 was fully characterized using various spectroscopic methods, such as X-ray single-crystal crystallography, 1H NMR spectroscopy, elemental analysis, FTIR spectroscopy, UV-vis spectroscopy, emission spectroscopy, EIS mass spectrometry, PXRD, and TGA analysis. The crystal structure of 2 reveals that the intermolecular hydrogen bonds between the peripheral pyridinium groups and the axially coordinated dihydrogen phosphate ligands are the main driving force for the supramolecular assembly. Simultaneously, the overall association of these chains in 2 leads to an open framework with porous channels. The photocatalytic degradation efficiency of methyl orange dye and tetracycline antibiotic by 2 was 83% within 75 min (rate constant = 0.023 min-1) and 75% within 60 min (rate constant = 0.018 min-1), respectively. The self-assembly of 2 resulted in a nanostructure with a huge surface area, elevated thermodynamic stability, interesting surface morphology, and excellent catalytic photodegradation performance for water pollutants, making these porphyrin-based photocatalytic systems promising for wastewater treatment.

Supramolecular Self-Assembled Nanostructures Derived from Amplified Structural Isomerism of Zn(II)-Sn(IV)-Zn(II) Porphyrin Triads and Their Visible Light Photocatalytic Degradation of Pollutants

Two structural isomeric porphyrin-based triads (Zn(II)porphyrin-Sn(IV)porphyrin-Zn(II)porphyrin) denoted as T1 and T2 were prepared from the reaction of meso-[5-(4-hydroxyphenyl)-10,15,20-tris(3,5-di-tert-butylphenyl)porphyrinato]zinc(II) (ZnL) with trans-dihydroxo-[5,10-bis(3-pyridyl)-15,20-bis(phenyl)porphyrinato]tin(IV) (SnP1) and trans-dihydroxo-[5,15-bis(3-pyridyl)-10,20-bis(phenyl)porphyrinato]tin(IV) (SnP2), respectively. All the compounds were characterized using UV-vis spectroscopy, emission spectroscopy, ESI-MS, 1H NMR spectroscopy, and FE-SEM. Most importantly, the two structurally isomeric porphyrin-based triads supramolecularly self-assembled into completely different nanostructures. T1 exhibits a nanosphere morphology, whereas T2 exhibits a nanofiber morphology. The amplified geometric feature in the structural isomeric porphyrin-based triads dictates the physical and chemical properties of the two triads. Both compounds showed the morphology-dependent visible light catalytic photodegradation of rhodamine B dye (74-97% within 90 min) and tetracycline antibiotic (44-71% within 45 min) in water. In both cases, the photodegradation efficiency of T2 was higher than that of T1. The present investigation can significantly contribute to the remediation of wastewater by tuning the conformational changes in porphyrin-based photocatalysts.

Recent Developments in Porphyrin-Based Metal-Organic Framework Materials for Water Remediation under Visible-Light Irradiation

Access to clean drinking water is a basic requirement, and eliminating pollutants from wastewater is important for saving water ecosystems. The porous structure and surface characteristics of metal-organic frameworks (MOFs) can function as a perfect scaffold for removing toxic compounds from wastewater. Porphyrins are promising building blocks for constructing MOFs. Porphyrin-based metal-organic frameworks (P-MOFs) have been fabricated using porphyrin ligands, metal clusters, or ions. These materials can harvest light from a wide region of the solar spectrum, and their framework morphology and physicochemical properties can be controlled by changing their peripheral subunits or metal ions. These porous crystalline materials have generated interest because of their distinctive characteristics, including large permanent porosity, interesting surface morphology, broad conformational diversity, high photostability, and semiconducting nature. This article discusses the recent progress and usefulness of P-MOFs. The fabrication procedures of P-MOFs are discussed, followed by the adsorptive and photocatalytic removal of contaminants from wastewater. The relationships between the geometries of P-MOFs and their light-harvesting and charge-transfer mechanisms for the photocatalytic degradation of pollutants are highlighted. Finally, some future perspectives and obstacles in the photodegradation usage of P-MOFs are discussed, along with feasible research directions to standardize efficient photocatalysts for improved photodegradation for water treatment.

Sn(IV)porphyrin-Incorporated TiO2 Nanotubes for Visible Light-Active Photocatalysis

In this study, two distinct photocatalysts, namely tin(IV)porphyrin-sensitized titanium dioxide nanotubes (SnP-TNTs) and titanium dioxide nanofibers (TNFs), were synthesized and characterized using various spectroscopic techniques. SnP-TNTs were formed through the hydrothermal reaction of NaOH with TiO2 (P-25) nanospheres in the presence of Sn(IV)porphyrin (SnP), resulting in a transformation into Sn(IV)porphyrin-imbedded nanotubes. In contrast, under similar reaction conditions but in the absence of SnP, TiO2 (P-25) nanospheres evolved into nanofibers (TNFs). Comparative analysis revealed that SnP-TNTs exhibited a remarkable enhancement in the visible light photodegradation of model pollutants compared to SnP, TiO2 (P-25), or TNFs. The superior photodegradation activity of SnP-TNTs was primarily attributed to synergistic effects between TiO2 (P-25) and SnP, leading to altered conformational frameworks, increased surface area, enhanced thermo-chemical stability, unique morphology, and outstanding visible light photodegradation of cationic methylene blue dye (MB dye). With a rapid removal rate of 95% within 100 min (rate constant = 0.0277 min-1), SnP-TNTs demonstrated excellent dye degradation capacity, high reusability, and low catalyst loading, positioning them as more efficient than conventional catalysts. This report introduces a novel direction for porphyrin-incorporated catalytic systems, holding significance for future applications in environmental remediation.