Visible-light-driven photocatalytic removal of acetaminophen from water using a novel MWCNT-TiO2-SiO2 photocatalysts

Modeling adsorption and photocatalytic treatment of recalcitrant contaminant on multi-walled carbon/TiO2 nanocomposite

A nanocomposite photocatalyst consisting of titanium dioxide (TiO2) supported on multiwalled carbon nanotubes (MWCNTs) has been successfully prepared and used for the treatment of wastewater contaminated with tetracycline (TC), a recalcitrant antibiotic pollutant. The TiO2/MCNT composites were prepared by a simple evaporation-drying method. The properties of MWCNT/TiO2 were optimized by dispersing different amounts of TiO2 onto MWCNT. The structural and optical characteristics of the nano-engineered photocatalyst composite were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR) techniques. Photocatalytic degradation of TC was conducted in a quartz glass reactor. Different kinetic models were used to demonstrate the governing mechanisms. The findings revealed that the TiO2/MWCNT composite had enhanced photocatalytic activity (95% TC removal) compared to TiO2 (86% removal). The photocatalyst nanocomposite exhibited overall pseudo-second-order reaction kinetics and favored the Langmuir adsorption isotherm. Although up to 95% degradation of TC was achieved, only 75% of it was mineralized as a result of the formation of stable refractory intermediates.

Simultaneous photooxidation and photoreduction of phenol and Cr(VI) ions using titania modified with nanosilica

The photocatalytic process of phenol oxidation and Cr(VI) reduction in the presence of nano-silica modified titania was carried out. The activity of composites was tested using two different light sources. The photocatalysts with 10% of nanosilica showed the highest activity. The calcination temperature (200–800 oC) significantly determined the sensitivity of the obtained materials to the light source used. Photocatalysts alternately adsorbed and desorbed Cr(VI) ions from the reaction mixture during irradiation. In the one-component mixture, complete oxidation of phenol was observed using material calcined at 650 oC, after 3 h of UV-VIS irradiation. In the reaction mixture of Cr(VI) and phenol, the highest activity was demonstrated by photocatalyst calcined at 300 oC. The concentration of phenol decreased in proportion to the decrease of chromium ions. The obtained titania-silica composites showed oxidizing properties towards phenol and reductive properties toward Cr(VI) ions.

Photocatalytic degradation of paracetamol and bisphenol A by chitosan supported covalent organic framework thin film with visible light irradiation

Covalent Organic Frameworks (COFs) have attracted extensive attention for the photocatalytic degradation of emerging organic contaminants. The difficulty in separation and recovery after use yet would hinder the practical application of COFs in powder form. In present study, COFs in film form were fabricated via using chitosan as the film-substrate to support COFs (CSCF). We found that CSCF could effectively degrade two types of emerging organic contaminants under visible light irradiation. Particularly, CSCF could effectively degrade 99.8% of paracetamol (PCT) and 94.0% of bisphenol A (BPA) within 180 min under visible light irradiation. •O₂^- and h⁺ played dominant roles during the photocatalytic degradation process. Hydroxylation and cleavage were the main degradation processes. CSCF exhibited good photocatalytic degradation performance in a broad range of ionic strengths, in the presence of common coexisting ions including Cl^-, NO₃^- and SO₄^2-, in a wide range of pH (5-11), and in real water samples including tap water, river water and lake water. Moreover, CSCF could be easily collected after use and exhibited excellent degradation performance in five successive cycles. CSCF has potential applications to treat water with either PCT or BPA contamination. This study provided a new insight into the practical application of COFs.

The inactivation effects and mechanisms of Karenia mikimotoi by non-metallic elements modified TiO2 (SNP-TiO2) under visible light

As an advanced oxidation technology, photocatalytic treatment of red tide algae pollution was potential of great research prospects. However, the most commonly used photocatalyst TiO₂ can only use ultraviolet light with short wavelength because of its wide band gap. In this study, the non-metallic elements S, N and P were added into the TiO₂ (SNP-TiO₂) lattice by hydrothermal synthesis, and the inactivation effects and mechanisms of Karenia mikimotoi were studied under visible light. The particle size of the obtained photocatalyst was about 10 nm. There were obvious characteristic peaks at the (101) (004) (200) (105) (211) (204) interface and included NO bond, PO bond and SO bond. The incorporation of S, N and P reduced the band gap of TiO₂ from 3.2 eV to 3.08 eV, which showed the integrity of the doping process. S_0.7N_1.4P_0.05-TiO₂ was full of excellent photocatalytic activity, the continuous inhibition effect was the most obvious. When exposed to 200 mg/L for 96 h, the growth inhibition rate (IR) was 81.8%. Photocatalytic process led to membrane damage of algal cells and collapse of photosynthetic system, caused oxidative stress response and accelerated algal cell inactivation. The study indicated that non-metallic elements modified TiO₂ (SNP-TiO₂) was full of potential of in treating red tide outbreak pollution under visible light.

Tunable TiO2-BN-Pd nanofibers by combining electrospinning and atomic layer deposition to enhance photodegradation of acetaminophen

The demand for fresh and clean water sources is increasing globally, and there is a need to develop novel routes to eliminate micropollutants and other harmful species from water. Photocatalysis is a promising alternative green technology that has shown great performance in the degradation of persistent pollutants. Titanium dioxide is the most used catalyst owing to its attractive physico-chemical properties, but this semiconductor presents limitations in the photocatalysis process due to the high band gap and the fast recombination of the photogenerated carriers. Herein, a novel photocatalyst has been developed, based on titanium dioxide nanofibers (TiO₂ NFs) synthesized by electrospinning. The TiO₂ NFs were coated by atomic layer deposition (ALD) to grow boron nitride (BN) and palladium (Pd) on their surface. The UV-Vis spectroscopy measurements confirmed the increase of the band gap and the extension of the spectral response to the visible range. The obtained TiO₂/BN/Pd nanofibers were then tested for photocatalysis, and showed a drastic increase of acetaminophen (ACT) degradation (>90%), compared to only 20% degradation obtained with pure TiO₂ after 4 h of visible light irradiation. The high photocatalytic activity was attributed to the good dispersion of Pd NPs on TiO₂-BN nanofibers, leading to a higher transfer of photoexcited hole carriers and a decrease of photogenerated electron-charge recombination. To confirm its reusability, recycling tests on the hybrid photocatalyst TiO₂/BN/Pd have been performed, showing a good stability over 5 cycles under UV and visible light. In addition, toxicity tests as well as quenching tests were carried out to check the toxicity of the byproducts formed and to determine active species responsible for the degradation. The results presented in this work demonstrate the potential of TiO₂/BN/Pd nanomaterials, and open new prospects for the preparation of tunable photocatalysts.

A review on carbon fiber-reinforced hierarchical composites: mechanical performance, manufacturing process, structural applications and allied challenges

The utilization of carbonaceous reinforcement-based polymer matrix composites in structural applications has become a hot topic in composite research. Although conventional carbon fiber-reinforced polymer composites (CFRPs) have revolutionized the composite industry by offering unparalleled features, they are often plagued with a weak interface and lack of toughness. However, the promising aspects of carbon fiber-based fiber hybrid composites and hierarchical composites can compensate for these setbacks. This review provides a meticulous landscape and recent progress of polymer matrix-based different carbonaceous (carbon fiber, carbon nanotube, graphene, and nanodiamond) fillers reinforced composites’ mechanical properties. First, the mechanical performance of neat CFRP was exhaustively analyzed, attributing parameters were listed down, and CFRPs’ mechanical performance barriers were clearly outlined. Here, short carbon fiber-reinforced thermoplastic composite was distinguished as a prospective material. Second, the strategic advantages of fiber hybrid composites over conventional CFRP were elucidated. Third, the mechanical performance of hierarchical composites based on carbon nanotube (1D), graphene (2D) and nanodiamond (0D) was expounded and evaluated against neat CFRP. Fourth, the review comprehensively discussed different fabrication methods, categorized them according to performance and suggested potential future directions. From here, the review sorted out three-dimensional printing (3DP) as the most futuristic fabrication method and thoroughly delivered its pros and cons in the context of the aforementioned carbonaceous materials. To conclude, the structural applications, current challenges and future prospects pertinent to these carbonaceous fillers reinforced composite materials were elaborated.

River water treatment using electrocoagulation for removal of acetaminophen and natural organic matter

Electrocoagulation (EC) was assessed for removal of acetaminophen and natural organic matter (measured as UV₂₅₄) from river water. Process was assessed for time, electrode materials, inter electrode distance, and voltage. Best conditions for removal of acetaminophen and UV₂₅₄ absorbance were 60 min reaction time, aluminum-aluminum electrodes, 2 cm inter electrode distance, and 9 V. Acetaminophen tested at 1, 2, 5, 10, and 20 mg L^-1 showed that treatment efficiency decreased as the concentration increased. The main mechanism for removal of acetaminophen was H bonding with Al(OH)₃ flocs; this was confirmed by XRD and FT-IR spectrum. Pseudo-second order kinetics model exhibited a good fit on experimental data for acetaminophen removal at different concentrations. Univariate ANOVA indicated statistically significant difference between treatments for acetaminophen removal (F_2.76 = 136, P = <0.001). A significant linear correlation was found between UV₂₅₄ absorbance and acetaminophen removal at different concentrations. Preliminary analysis suggest that EC will cost US$ 0.22/m³ for river water treatment. The lab-scale EC process was compared with a full-scale water treatment plant for removal of natural organic matter. Water treatment plant after multiple levels of purification was not able to fully remove UV₂₅₄ absorbance whereas EC treatment showed good efficiency.

Photodegradation of Pharmaceutical and Personal Care Products (PPCPs) and Antibacterial Activity in Water by Transition Metals

The intensity of emerging pollutants such as pharmaceuticals and personal care products (PPCPs) in the aquatic and terrestrial environment is a major source of concern to researchers. The current conventional methods of wastewater treatment plants are considered not efficient enough in the complete removal of the recalcitrant contaminants from water. The use of modified transition metals in visible responsive synthesis to degrade PPCPs and other pollutants (organic and inorganic) is considered as a developing green chemistry and sustainable technology. Hence, this review presents the state-of-the-art discussion on the novel photodegradation of PPCPs, and antibacterial activities of transition metal-modified magnetite materials for wastewater treatment, and suggested directions for the future. Transition metal-modified magnetite nanostructured photocatalysis is identified as one of the best candidates employed in advanced oxidation processes (AOPs) for wastewater treatment and has been found to efficiently destroy bacterial spores and effectively remove recalcitrant pollutants in water. Therefore, this article hopes to contribute scientific knowledge along with existing ones on advanced mechanisms and technology used in wastewater treatment.

AgI modified covalent organic frameworks for effective bacterial disinfection and organic pollutant degradation under visible light irradiation

Covalent organic frameworks (COFs) have recently been demonstrated to have great application potentials in water treatment. Their photocatalytic performance towards bacterial disinfection and organic pollutant degradation yet has seldom been investigated. In this study, AgI modified COFs (using 2,5-diaminopyridine and 1,3,5-triformylphloroglucinol as precursors) (COF-PD/AgI) were fabricated and their applications to photocatalytically disinfect bacteria and degrade organic pollutants were investigated. COF-PD/AgI exhibited effective photocatalytic performance towards Escherichia coli disinfection and organic pollutant (Rhodamine B and acetaminophen) degradation. SEM images were employed to investigate cell disinfection process, while theoretical density functional theory (DFT) calculation and intermediates determination were used to elucidate organic pollutant degradation processes. Scavenger experiments, ESR spectra and chemical probes experiments confirmed O₂^-, h⁺ and OH played important roles in the photocatalytic process. The formation of dual-band Z-scheme heterojunction improved photocatalytic performance. COF-PD/AgI remained high photocatalytic activity in the four consecutive cycles and could serve as a promising photocatalyst for water purification.

Activated Carbon from Agricultural Wastes for Adsorption of Organic Pollutants

Agricultural waste materials (strawberry seeds and pistachio shells) were used for preparation of activated carbons by two various methods. Chemical activation using acetic acid and physical activation with gaseous agents (carbon dioxide and water vapor) were chosen as mild and environmentally friendly methods. The effect of type of raw material, temperature, and activation agent on the porous structure characteristics of the materials was discussed applying various methods of analysis. The best obtained activated carbons were characterized by high values of specific surface area (555-685 m²/g). The Guinier analysis of small-angle X-ray scattering (SAXS) curves showed that a time of activation affects pore size. The samples activated using carbon dioxide were characterized mostly by the spherical morphology of pores. Adsorbents were utilized for removal of the model organic pollutants from the single- and multicomponent systems. The adsorption capacities for the 4-chloro-2-methyphenoxyacetic acid (MCPA) removal were equal to 1.43-1.56 mmol/g; however, for adsorbent from strawberry seeds it was much lower. Slight effect of crystal violet presence on the MCPA adsorption and inversely was noticed as a result of adsorption in different types of pores. For similar herbicides strong competition in capacity and adsorption rate was observed. For analysis of kinetic data various equations were used.

Solvothermal synthesis of multiwall carbon nanotubes/BiOI photocatalysts for the efficient degradation of antipyrine under visible light

Antipyrine (ANT), as a widely used relieve headache, fever anti-inflammatory pharmaceutical in medical treatment, is difficult to be removed completely in water. The application of photocatalytic removal of ANT is restricted to UV light irradiation (<5% of solar energy), and the degradation pathways of ANT require more theoretical evidence. In this study, a series of three dimensions (3D) hierarchical structure multiwall carbon nanotubes/bismuth oxyiodide (MWCNTs/BiOI) photocatalysts were systematically designed and firstly applied to remove ANT through visible light (>43% of solar energy) induced photodegradation. Consequently, the as-prepared MWCNTs/BiOI photocatalysts presented superior photocatalytic activities on ANT degradation with respect to that of BiOI under 60 min visible light irradiation (100% vs 82.2%). Especially, the enhanced photocatalytic mechanism on ANT was analyzed by morphology, optical and photo-electrochemical properties. Results revealed that the designed 3D micro-mesoporous structure could promote the diffusion of photogenerated electron-hole pairs, and the utilization of photoelectrons could be efficiently improved by MWCNTs (1.5 times). Furthermore, based on radicals scavenging experiments, the photogenerated hole (h⁺) and superoxide radical (O₂^-) were demonstrated as the dominant active species in ANT photocatalytic oxidation process. The photodegradation pathways of ANT were proposed with the calculation of frontier electron densities (FEDs) and the analysis of LC-MS/MS. This study presents a feasible approach for the high efficiency removal of trace pharmaceuticals under visible light photocatalytic process.

Novel cadmium oxide-graphene nanocomposite grown on mesoporous silica for simultaneous photocatalytic H2-evolution

Novel Cadmium Oxide-Graphene Nanocomposite Grown on Mesoporous Silica have been successfully prepared using a self-assembly method under the catering of cetyltrimethylammonium bromide (CTAB) as the surfactant template at ambient conditions. The structural and optical properties of the obtained nanocomposites were investigated by many different techniques. The results of photocatalytic measurements revealed that almost 100% of MB organic dye was removed with the presence of SiO₂/CdO-graphene composite under visible light irradiation. Moreover, the initial pH also plays an important role in the photodegradation processes. On the other hand, this work opens a way to enhance the photocatalytic activity of gallic acid at ambient conditions without any further different oxidation processes. From the evolutionary aspect, SiO₂/CdO-graphene composite revealed better H₂ generation than that of binary photocatalyst (CdO-graphene nanocomposite). The results of characterization and photodegradation suggest that SiO₂/CdO-graphene material constitutes a new photocatalyst for the degradation of organic contaminants, as well as the development of an efficient hetero-system for hydrogen production.