Integrated photocatalysis adsorption processes for oxytetracycline removal: using volborthite and its composite with g-C3N4.

The photocatalytic-adsorption performance of the composites of volborthite (CuVA) and graphitic carbon nitride (g-C3N4) was studied in this work using oxytetracycline (OTC) as model pollutant under LED light irradiation. CuVA at different weight percentages (10, 30, 50), namely, C10, C30, and C50, were loaded onto graphitic carbon nitride using wet chemical method. The physical, chemical, and optical properties were evaluated via various analytical techniques. Through integrated adsorption-photocatalytic process, no significant photocatalytic reaction occurred in g-C3N4 and the composite even after 4 h of irradiation. The setup was modified such that each run was conducted in the presence and absence of light. Aside from photolysis and g-C3N4, all composites performed better under the presence of light in which CuVA improved the most from ~ 50% down to ~ 20% of initial concentration. CuVA performed almost identically (80% removal of OTC) under the presence of light irradiation at ambient temperature (22 °C) and in the dark at 32 °C, confirming that temperature was the contributing factor to the improvement instead of light. CuVA exhibited excellent adsorption capacity of 171 mg/g and adsorption rate of 90% towards the removal of highly concentrated OTC (100 mg/L) under optimized parameters of pH 5.0 and at 42 °C after 3 h of adsorption process. Life cycle assessment revealed that close to 50% of fresh 100 ppm OTC could be removed after five cycles without any desorption process.

Accelerated sunlight photocatalysis through improved electron mobility between g-C3N4 and BiPO4 nanomaterial.

Herein, we report a detailed study on creating heterojunction between graphitic carbon nitride (g-C3N4) and bismuth phosphate (BiPO4), enhancing the unpaired free electron mobility. This leads to an accelerated photocatalysis of 2,4-dichlorophenols (2,4-DCPs) under sunlight irradiation. The heterojunction formation was efficaciously conducted via a modest thermal deposition technique. The function of g-C3N4 plays a significant role in generating free electrons under sunlight irradiation. Together, the generated electrons at the g-C3N4 conduction band (CB) are transferred and trapped by the BiPO4 to form active superoxide anion radicals (•O2-). These active radicals will be accountable for the photodegradation of 2,4-DCPs. The synthesized composite characteristics were methodically examined through several chemical and physical studies. Due to the inimitable features of both g-C3N4 and BiPO4, its heterojunction formation, 2.5wt% BiPO4/g-C3N4 achieved complete 2,4-DCP removal (100%) in 90 min under sunlight irradiation. This is due to the presence of g-C3N4 that enhanced electron mobility through the formation of heterojunctions that lengthens the electron-hole pairs' lifetime and maximizes the entire solar spectrum absorption to generate active electrons at the g-C3N4 conduction band. Thus, this formation significantly draws the attention for future environmental remediation, especially in enhancing the entire solar spectrum's harvesting.

Novel Carbon Quantum Dots/Silver Blended Polysulfone Membrane with Improved Properties and Enhanced Performance in Tartrazine Dye Removal.

This study produced a novel polysulfone (PSF) membrane for dye removal using lemon-derived carbon quantum dots-grafted silver nanoparticles (Ag/CQDs) as membrane nanofiller. The preparation of CQDs was completed by undergoing hydrothermal treatment to carbonize the pulp-free lemon juice into CQD solution. The CQD solution was then coupled with Ag nanoparticles to form Ag/CQDs nanohybrid. The synthesized powders were characterized in terms of morphologies, functional groups and surface charges. A set of membranes was fabricated with different loadings of Ag/CQDs powder using the nonsolvent-induced phase separation (NIPS) method. The modified membranes were studied in terms of morphology, elemental composition, hydrophilicity and pore size. In addition, pure water flux, rejection test and fouling analysis of the membranes were evaluated using tartrazine dye. From the results, 0.5 wt % of Ag/CQD was identified as the optimum loading to be incorporated with the pristine PSF membrane. The modified membrane exhibited an excellent pure water permeability and dye rejection with improvements of 169% and 92%, respectively. In addition, the composite membrane also experienced lower flux decline, higher reversible fouling and lower irreversible fouling. This study has proven that the addition of CQD additives into membrane greatly improves the polymeric membrane's properties and filtration performance.

An overview of photocatalytic degradation: photocatalysts, mechanisms, and development of photocatalytic membrane.

Photocatalysis is an ecofriendly technique that emerged as a promising alternative for the degradation of many organic pollutants. The weaknesses of the present photocatalytic system which limit their industrial applications include low-usage of visible light, fast charge recombination, and low migration ability of the photo-generated electrons and holes. Therefore, various elements such as noble metals and transition metals as well as non-metals and metalloids (i.e., graphene, carbon nanotube, and carbon quantum dots) are doped into the photocatalyst as co-catalysts to enhance the photodegradation performance. The incorporation of the co-catalyst which alters the photocatalytic mechanism was discussed in detail. The application of photocatalysts in treating persistent organic pollutants such as pesticide, pharmaceutical compounds, oil and grease and textile in real wastewater was also discussed. Besides, a few photocatalytic reactors in pilot scale had been designed for the effort of commercializing the system. In addition, hybrid photocatalytic system integrating with membrane filtration together with their membrane fabrication methods had also been reviewed. This review outlined various types of heterogeneous photocatalysts, mechanism, synthesis methods of biomass supported photocatalyst, photocatalytic degradation of organic substances in real wastewater, and photocatalytic reactor designs and their operating parameters as well as the latest development of photocatalyst incorporated membrane.

Amalgamation of N-graphene quantum dots with nanocubic like TiO2: an insight study of sunlight sensitive photocatalysis.

In this work, a sunlight-sensitive photocatalyst of nanocubic-like titanium dioxide (TiO2) and N-doped graphene quantum dots (N-GQDs) is developed through a simple hydrothermal and physical mixing method. The successful amalgamation composite photocatalyst characteristics were comprehensively scrutinized through various physical and chemical analyses. A complete removal of bisphenol A (BPA) is attained by a synthesized composite after 30 min of sunlight irradiation as compared to pure TiO2. This clearly proved the unique contribution of N-GQDs that enhanced the ability of light harvesting especially under visible light and near-infrared region. This superior characteristic enables it to maximize the absorbance in the entire solar spectrum. However, the increase of N-GQDs weight percentage has created massive oxygen vacancies that suppress the generation of active radicals. This resulted in a longer duration for a complete removal of BPA as compared to lower weight percentage of N-GQDs. Hence, this finding can offer a new insight in developing effective sunlight-sensitive photocatalysts for various complex organic pollutants degradation.

M/g-C3N4 (M=Ag, Au, and Pd) composite: synthesis via sunlight photodeposition and application towards the degradation of bisphenol A.

In this work, natural sunlight successfully induced the deposition of gold (Au), silver (Ag), and palladium (Pd) nanoparticles (NPs) with 17.10, 9.07, and 12.70 wt% onto the surface of graphitic carbon nitride (g-C3N4). The photocatalytic evaluation was carried out by adopting Bisphenol A (BPA) as a pollutant under natural sunlight irradiation. The presence of noble metals was confirmed by EDX, HRTEM, and XPS analysis. The deposition of Ag NPs (7.9 nm) resulted in the degradation rate which was 2.15-fold higher than pure g-C3N4 due to its relatively small particle size, contributing to superior charge separation efficiency. Au/g-C3N4 unveiled inferior photoactivity because the LSPR phenomenon provided two pathways for electron transfer between Au NPs and g-C3N4 further diminished the performance. The improved degradation lies crucially on the particle size and Schottky barrier formation at the interface of M/g-C3N4 (M=Au, Ag, and Pd) but not the visible light harvesting properties. The mechanism insight revealed the holes (h+) and superoxide radical (•O2-) radical actively involved in photocatalytic reaction for all composites.

Mechanistic insights into plasmonic photocatalysts in utilizing visible light.

The utilisation of sunlight as an abundant and renewable resource has motivated the development of sustainable photocatalysts that can collectively harvest visible light. However, the bottleneck in utilising the low energy photons has led to the discovery of plasmonic photocatalysts. The presence of noble metal on the plasmonic photocatalyst enables the harvesting of visible light through the unique characteristic features of the noble metal nanomaterials. Moreover, the formation of interfaces between noble metal particles and semiconductor materials further results in the formation of a Schottky junction. Thereby, the plasmonic characteristics have opened up a new direction in promoting an alternative path that can be of value to the society through sustainable development derived through energy available for all for diverse applications. We have comprehensively prepared this review to specifically focus on fundamental insights into plasmonic photocatalysts, various synthesis routes, together with their strengths and weaknesses, and the interaction of the plasmonic photocatalyst with pollutants as well as the role of active radical generation and identification. The review ends with a pinnacle insight into future perspectives regarding realistic applications of plasmonic photocatalysts.

Sugarcane juice derived carbon dot-graphitic carbon nitride composites for bisphenol A degradation under sunlight irradiation.

Carbon dots (CDs) and graphitic carbon nitride (g-C3N4) composites (CD/g-C3N4) were successfully synthesized by a hydrothermal method using urea and sugarcane juice as starting materials. The chemical composition, morphological structure and optical properties of the composites and CDs were characterized using various spectroscopic techniques as well as transmission electron microscopy. X-ray photoelectron spectroscopy (XPS) results revealed new signals for carbonyl and carboxyl groups originating from the CDs in CD/g-C3N4 composites while X-ray diffraction (XRD) results showed distortion of the host matrix after incorporating CDs into g-C3N4. Both analyses signified the interaction between g-C3N4 and CDs. The photoluminescence (PL) analysis indicated that the presence of too many CDs will create trap states at the CD/g-C3N4 interface, decelerating the electron (e-) transport. However, the CD/g-C3N4(0.5) composite with the highest coverage of CDs still achieved the best bisphenol A (BPA) degradation rate at 3.87 times higher than that of g-C3N4. Hence, the charge separation efficiency should not be one of the main factors responsible for the enhancement of the photocatalytic activity of CD/g-C3N4. Instead, the light absorption capability was the dominant factor since the photoreactivity correlated well with the ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) results. Although the CDs did not display upconversion photoluminescence (UCPL) properties, the π-conjugated CDs served as a photosensitizer (like organic dyes) to sensitize g-C3N4 and injected electrons to the conduction band (CB) of g-C3N4, resulting in the extended absorption spectrum from the visible to the near-infrared (NIR) region. This extended spectral absorption allows for the generation of more electrons for the enhancement of BPA degradation. It was determined that the reactive radical species responsible for the photocatalytic activity were the superoxide anion radical (O2•-) and holes (h+) after performing multiple scavenging tests.

Mechanistic Characteristics of Surface Modified Organic Semiconductor g-C3N4 Nanotubes Alloyed with Titania.

The visible-light-driven photocatalytic degradation of Bisphenol A (BPA) was investigated using the binary composite of alkaline treated g-C3N4 (HT-g-C3N4) deposited over commercial TiO2 (Evonik Degussa GmbH, Essen, Germany). The existence and contribution of both TiO2 and g-C3N4/HT-g-C3N4 in the composite was confirmed through various analytical techniques including powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectra (UV-vis-DRS), and photoluminescence (PL) analysis. The results showed that the titania in the binary composite exhibited both pure rutile and anatase phases. The morphological analysis indicated that the spongy "morel-like" structure of g-C3N4 turned to nanotube form after alkaline hydrothermal treatment and thereby decreased the specific surface area of HT-g-C3N4. The low surface area of HT-g-C3N4 dominates its promising optical property and effective charge transfer, resulting in a deprived degradation efficiency of BPA two times lower than pure g-C3N4. The binary composite of HT-g-C3N4/TiO2 exhibited excellent degradation efficiency of BPA with 2.16 times higher than the pure HT-g-C3N4. The enhanced photocatalytic activity was mainly due to the promising optical band gap structure with heterojunction interface, favorable specific surface area, and good charge separation.

Post-treatment of palm oil mill effluent (POME) using combined persulphate with hydrogen peroxide (S2O82-/H2O2) oxidation.

The aim of the current study is to evaluate the effectiveness of combined persulphate with hydrogen peroxide (S2O82-/H2O2) oxidation as a post-treatment of biologically treated palm oil mill effluent (POME) for the first time in the literature. The removal efficiencies of chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N), and suspended solids (SS) were 36.8%, 47.6%, and 90.6%, respectively, by S2O82- oxidation alone under certain operation conditions (i.e., S2O82- = 0.82 g, pH 11, and contact time 20 min). Nevertheless, the combined process (S2O82-/H2O2) achieved 75.8% and 87.1% removals of NH3-N and SS, respectively, under 2.45/1.63 g/g H2O2/S2O82-, pH 11, and 20 min oxidation. Moreover, 56.9% of COD was removed at pH 8.4.

Synthesis, features and solar-light-driven photocatalytic activity of TiO2 nanotube arrays loaded with SnO2.

In the present study TiO2 nanotube arrays (TNTs) were loaded with a post-transition metal oxide particles namely SnO2 via incipient wet impregnation method by varying its concentration (1.59 wt%, 2.25 wt% and 2.84 wt%). The photocatalytic activity of the prepared photocatalyst was evaluated for the degradation of methylene blue (MB) in presence of natural solar light irradiation. The morphological analyses revealed that the prepared TNTs had average inner diameter of 109 nm, wall thickness of 15 nm and tube length of 7-10 µm, respectively, while the crystalline phase and Raman spectra confirmed the 100% anatase mineral form of TiO2. Further, the presence of SnO2 in TNTs was confirmed by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The visible light absorption properties of TNTs improved drastically with increasing SnO2 loadings. The coupling effect of SnO2 and TiO2 significantly enhanced degradation efficiency of MB. An 84% degradation of MB was achieved in 6 h of irradiation under clear sky condition.