Advances in photocatalytic degradation of organic pollutants in wastewaters: harnessing the power of phthalocyanines and phthalocyanine-containing materials

Access to clean water is increasingly challenging worldwide due to human activities and climate change. Wastewater treatment and utilization offer a promising solution by reducing the reliance on pure underground water. However, it is crucial to develop efficient and sustainable methods for wastewater purification. Among the emerging wastewater treatment strategies, photocatalysis has gained significant attention for decomposing organic pollutants in water, especially when combined with sunlight and a recoverable photocatalyst. Heterogeneous photocatalysts have distinct advantages, as they can be recovered and reused without significant loss of activity over multiple cycles. Phthalocyanine dyes, with their exceptional photophysical properties, are particularly valuable for homogeneous and heterogeneous photocatalysis. By immobilizing these photosensitizers in various supports, hybrid materials extend their light absorption into the visible spectrum, complementing most supports' limited UV light absorption. The novelty and research importance of this review stems from its discussion of the multifaceted approach to treating contaminated wastewater with phthalocyanines and materials containing phthalocyanines. It highlights key aspects of each study, including photocatalytic efficiency, recyclability characteristics, investigation of the generation of oxygen species responsible for degradation, identification of the major degradation byproducts for each pollutant, and others. Moreover, the review includes tables that illustrate and compare the various phthalocyanines and supporting materials employed in each study for pollutant degradation. Additionally, almost all photocatalysts mentioned in this review could degrade at least 5% of the pollutant, and more than 50 photocatalysts showed photocatalytic rates above 50%. When immobilized in some support, the synergistic effect of the phthalocyanine was visible in the photocatalytic rate of the studied pollutant. However, when performing these types of works, it is necessary to understand the degradation products of each pollutant and their relative toxicities. Along with this, recyclability and stability studies are also necessary. Despite the good results presented in this review, some of the works lack those studies. Moreover, none of the works mentions any study in wastewater.

Preparation of metal-free BP/CN photocatalyst with enhanced ability for photocatalytic tetracycline degradation

The successful application of photocatalysis in practical water treatment opreations relies greatly on the development of highly efficient, stable and low-cost photocatalysts. The low-cost metal-free photocatalyst made up of black phosphorus (BP) and graphitic carbon nitride (CN) was successfully constructed and firstly used for the photocatalytic treatment of antibiotic contaminants in this work. Compared with bare CN, the BP/CN photocatalyst exhibited the enhanced photocatalytic performance for tetracycline hydrochloride (HTC) degradation, that 99% of HTC was removed by 6BP/CN (doping amount of BP was 6%) within 30 min under the simulated visible-light irradiation. The efficiency was even comparable to those of some high-efficiency photocatalysts recently-reported such as Fe⁰@POCN, CuInS₂/Bi₂MoO₆ and Cu₂O@HKUST-1. Under natural sunlight illumination, the determined apparent rate constant for degradation of HTC by BP/CN was 2.7 times as that by P25 TiO₂. The experimental results indicated that loading BP on CN could enhance the separation of charge carriers and promote the ability of light absorption for visible-light, thus leading to a greater catalytic activity. Meanwhile, the influences of different operating variables (pH, water, ion and HTC concentration) on HTC degradation were studied in detail. Furthermore, the degradation pathway of HTC was also proposed. In addition, the photocatalytic activity of the BP/CN for production of hydrogen peroxide (H₂O₂) was also studied, which could reach up to 501.04 μmol g^-1h^-1. It is anticipated that BP/CN photocatalyst could be used for practical water treatment.

Unveiling the visible-light-driven photodegradation pathway and products toxicity of tetracycline in the system of Pt/BiVO4 nanosheets

The antibiotics pollution has currently captured increasing concerns due to its potential hazards to the environment and human health. The development of efficient and viable techniques for the removal of antibiotics is one of the research hotspots in fields of wastewater treatment and pharmaceutical industry. Although the photodegradation of antibiotics is widely studied, the evolution and toxicity of degradation intermediates have been rarely documented. Herein, Pt nanoparticles (NPs) decorated BiVO₄ nanosheets (Pt/BiVO₄ NSs) that exhibit excellent tetracycline (TC) photodegradation activity and stability have been prepared. Especially, the TC degradation efficiency reaches ca. 88.5% after 60 min under visible light irradiation, which is superior to most of the metal loaded two-dimensional photocatalysts reported hitherto. The excellent photocatalytic activity is attributable to the enhanced light absorption capacity and charge separation efficiency in Pt/BiVO₄ NSs. h⁺, •O₂^- and •OH are the main active species for TC degradation, resulting in three possible degradation pathways. Furthermore, we first verify that TC solutions treated by Pt/BiVO₄ NSs are harmless to Escherichia coli K-12 and various bacteria in natural rivers, which would not stimulate Escherichia coli to produce antibiotics resistance genes (ARGs). This work develops an environmentally friendly photodegradation strategy using Pt/BiVO₄ NSs with potentials for efficient remediation of antibiotics pollution in wastewater.

All-solid-state Z-scheme Ag3PO4/CSs/AgBr heterostructures for efficient visible-light photocatalysis and the photocatalytic mechanism

A novel solid-state Z-scheme photocatalyst Ag₃PO₄/CSs/AgBr (carbon spheres, CSs) was rationally designed and successfully synthesized via a facile hydrothermal coprecipitation reaction. AgBr and Ag₃PO₄ were effectively loaded on the surface of the CSs and Ag₃PO₄/CSs/AgBr showed wide visible light absorption and superior photocatalytic performance. On the basis of ultraviolet photoelectron spectroscopy (UPS) analysis and scavenger reactions, a possible photocatalytic reaction mechanism for Ag₃PO₄/CSs/AgBr is proposed. The CSs act as a charge carrier transfer bridge for constructing the all-solid-state Z-scheme photocatalyst. The photogenerated electrons from Ag₃PO₄ and holes from AgBr congregate and recombine in the CSs phase, leaving photogenerated electrons with strong reduction abilities in the conduction band (CB) of AgBr and holes with strong oxidation abilities in the valence band (VB) of Ag₃PO₄. Some Ag⁺ ions accept electrons and turn to Ag nanoparticles (NPs), leading to the surface plasmon resonance of Ag NPs on AgBr. Therefore, the photocatalytic performance and stability were significantly improved.

Oxidative Degradation of Pharmaceuticals: The Role of Tetrapyrrole-Based Catalysts

Nowadays, society’s widespread consumption of pharmaceutical drugs and the consequent accumulation of such compounds or their metabolites in effluents requires the development of efficient strategies and systems that lead to their effective degradation. This can be done through oxidative processes, in which tetrapyrrolic macrocycles (porphyrins, phthalocyanines) deserve special attention since they are among the most promising degradation catalysts. This paper presents a review of the literature over the past ten years on the major advances made in the development of oxidation processes of pharmaceuticals in aqueous solutions using tetrapyrrole-based catalysts. The review presents a brief discussion of the mechanisms involved in these oxidative processes and is organized by the degradation of families of pharmaceutical compounds, namely antibiotics, analgesics and neurological drugs, among others. For each family, a critical analysis and discussion of the fundamental roles of tetrapyrrolic macrocycles are presented, regarding both photochemical degradative processes and direct oxidative chemical degradation.

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.

Immobilized TiO2/ZnO Sensitized Copper (II) Phthalocyanine Heterostructure for the Degradation of Ibuprofen under UV Irradiation

Photocatalytic coatings of TiO2/ZnO/CuPc were developed on stainless steel substrates by subsequent sol gel dip coating for TiO2, spray pyrolysis for ZnO, and spin coating for copper (ii) phthalocyanine (CuPc) deposition. The latter compound was successfully prepared using a Schiff-based process. The materials and coatings developed were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy with attached energy dispersive spectroscopy (SEM-EDS), UV-Vis spectroscopy, room temperature photoluminescence (RTPL) spectroscopy, H1-nuclear magnetic resonance (1H-NMR) spectroscopy, C13-nuclear magnetic resonance (13C-NMR) spectroscopy, and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS). The as-deposited TiO2/ZnO/CuPc on stainless steel retained in pristine state the structural and morphological/spectroscopic characteristics of its respective components. Estimated energy band gap values were 3.22 eV, 3.19 eV, 3.19 eV for TiO2, ZnO, TiO2/ZnO respectively and 1.60 eV, 2.44 eV, and 2.92 eV for CuPc. The photocatalytic efficiency of the fabricated TiO2/ZnO/CuPc coatings was tested toward ibuprofen (IBF). After 4 h irradiation under 365 nm UV, an increased degradation of about 80% was achieved over an initial 5 mg/L ibuprofen (IBF). This was much higher compared to about 42% and 18% IBF degradation by TiO2/ZnO and TiO2 thin film, respectively. In all cases, the stability of the best-performing photocatalyst was investigated showing a small decline to 77% of IBF degradation after the 5th cycle run. The effect of pH, reactive oxygen species (ROS) probe, shed light on a possible catalytic mechanism that was suggested.

Integration of perovskite type Bi2MoO6 nanosheets onto one dimensional CdS: a type-II heterostructured photocatalytic system for efficient charge separation in the hydrogen evolution reaction

Bi₂MoO₆ nanosheets were assembled onto CdS nanorods and the resultant CdS-Bi₂MoO₆ core–shell heterostructures were utilized for efficient H₂ evolution reaction.