Nickel (Ni), cobalt (Co), and zinc (Zn) loaded on fibrous silica KCC-1 was investigated for CO2 methanation reactions. Ni/KCC-1 exhibits the highest catalyst performance with a CH4 formation rate of 33.02 × 10-2 molCH4 molmetal-1 s-1, 1.77 times higher than that of Co/KCC-1 followed by Zn/KCC-1 and finally the parent KCC-1. A pyrrole adsorption FTIR study reveals shifting of perturbed N-H stretching decreasing slightly with the addition of metal oxide, suggesting that the basic sites of catalyst were inaccessible due to metal oxide deposition. The strengths of basicity were found to follow sthe equence KCC-1, Ni/KCC-1, Zn/KCC-1, and Co/KCC-1. The data were supported by N2 adsorption desorption analysis, where Co/KCC-1 displayed the greatest reduction in total surface area whereas Ni/KCC-1 displayed the least reduction. The elucidation of difference mechanism pathways has also been studied by in situ IR spectroscopy studies to determine the role of different metal oxides in CO2 methanation. It was discovered that Ni/KCC-1 and Co/KCC-1 follow a dissociative mechanism of CO2 methanation in which the CO2 molecule was dissociated on the surface of the metal oxide before migration onto the catalyst surface. This was confirmed by the evolution of a peak corresponding to carbonyl species (COads) on a metal oxide surface in FTIR spectra. Zn/KCC-1, on the other hand, showed no such peak, indicating associative methanation pathways where a hydrogen molecule interacts with an O atom in CO2 to form COads and OH. These results offers a better understanding for catalytic studies, particularly in the field of CO2 recycling.
Phosphate and nitrate were loaded on silica BEA (P/HSi@BEA and N/HSi@BEA), which is fibrously protonated by the impregnation method for n-hexane and cyclohexane isomerization. The characterization analysis specified the removal of tetrahedral aluminum atoms in the framework, which was triggered by the existence of phosphate and nitrate groups in the catalyst. The exchanged role of Si(OH)Al to P-OH as active acidic sites in the P/HSi@BEA catalyst reduced its acidic strength, which was confirmed by the FTIR results. Lewis acidic sites of P/HSi@BEA performance are a significant part in the generation of high protonic acid sites, as proven by the in situ ESR study. However, FTIR evacuation and 27Al NMR revealed that the reduction in the amount of extraframework Al (EFAl) is due to its interaction with the nitrate group on the outside of the catalyst surface. The N/HSi@BEA catalyst exhibited high acidic strength because of the existence of more Si(OH)Al, which was initiated during the nitrate-incorporation process. Of significance is that the catalytic performance of n-hexane isomerization in the presence of hydrogen reached 50.3% product isomer yield at 250 °C, which might be ascribed to the presence of P-OH active sites that are responsible for accepting electrons, forming active protonic acid sites. NO3-EFAl interaction induced the formation of Brønsted acid sites, and higher mesopore volume favors the production of cyclohexane isomers up to 48.4% at 250 °C. This fundamental study exhibits that significant interactions given by such phosphate and nitrate groups with the unique silica fibrous BEA support could enhance isomerization, which contributes to the high quality of fuel.
Nanostructured photocatalysts commonly offered opportunities to solve issues scrutinized with the environmental challenges caused by steep population growth and rapid urbanization. This photocatalyst is a controllable characteristic, which can provide humans with a clean and sustainable ecosystem. Over the last decades, one of the current thriving research focuses on visible-light-driven CeO2-based photocatalysts due to their superior characteristics, including unique fluorite-type structure, rigid framework, and facile reducing oxidizing properties of cerium's tetravalent (Ce4+) and trivalent (Ce3+) valence states. Notwithstanding, owing to its inherent wide energy gap, the solar energy utilization efficiency is low, which limits its application in wastewater treatment. Numerous modifications of CeO2 have been employed to enhance photodegradation performances, such as metals and non-metals doping, adding support materials, and coupling with another semiconductor. Besides, all these doping will form a different heterojunction and show a different way of electron-hole migration. Compared to conventional heterojunction, advanced heterojunction types such as p-n heterojunction, Z-scheme, Schottky junction, and surface plasmon resonance effect exhibit superior performance for degradation owing to their excellent charge carrier separation, and the reaction occurs at a relatively higher redox potential. This review attends to providing deep insights on heterojunction mechanisms and the latest progress on photodegradation of various contaminants in wastewater using CeO2-based photocatalysts. Hence, making the CeO2 photocatalyst more foresee and promising to further development and research.
With the tremendous development of the economy and industry, the pollution of water is becoming more serious due to the excessive chemical wastes that need to remove thru reduction or oxidation reactions. Simultaneous removal of dual pollutants via photocatalytic redox reaction has been tremendously explored in the last five years due to effective decontamination of pollutants compared to a single pollutants system. In a photocatalysis mechanism, the holes in the valence band can remarkably promote the oxidation of a pollutant. At the same time, photoexcited electrons are also consumed for the reduction reaction. The synergistic between the reduction and oxidation inhibits the recombination of electron-hole pairs extending their lifetime. In this review, the binary pollutants that selectively removed via photocatalysis reduction or oxidation are classified according to heavy metal-organic pollutant (HM/OP), heavy metal-heavy metal (HM/HM) and organic-organic pollutants (OP/OP). The intrinsic between the pollutants was explained in three different mechanisms including inhibition of electron-hole recombination, ligand to metal charge transfer and electrostatic attraction. Several strategies for the enhancement of this treatment method which are designation of catalysts, pH of mixed pollutants and addition of additive were discussed. This review offers a recent perspective on the development of photocatalysis system for industrial applications.
Conversion of lignocellulosic biowastes from agricultural industry into nanocrystalline cellulose provides pathway to reduce environmental pollution while enhancing the economic value of biowastes. Nanocellulose (NCC) with uniform morphology was isolated from pepper (Piper nigrum L.) stalk waste (PW) using acid hydrolysis method. The role of inorganic acids (sulfuric acid, hydrochloric acid, phosphoric acid), organic acids (oxalic acid, citric acid, acetic acid) and variation of sonication times were investigated on the physicochemical characteristics, self-assembled structure, crystallinity, particle size, zeta potential and thermal stability of the isolated nanocellulose. Hydrolysis using inorganic acids transformed cellulose from PW into a spherical shaped NCC at ~33-67 nm of average diameter. Meanwhile hydrolysis in organic acids produced rod-shaped NCC at 210-321 nm in length. This study highlighted the role of acidity strength for organic acid and inorganic acid in controlling the level of hydrogen bond dissociation and the dissolution of amorphous fragments, which consequently directing the morphology and the physicochemical properties of NCCs.
Recently, hetero junction materials (p-n-p and n-p-n) have been developed for uplifting the visible light activity to destroy the harmful pollutants in wastewater. This manuscript presents a vivid description of novel n-p-n junction materials namely CeO2-PPy-ZnO. This novel n-p-n junction was applied as the photocatalyst in drifting the mobility of charge carriers and hence obtaining the better photocatalytic activity when compared with p-n and pure system. Such catalyst's syntheses were successful via the copolymerization method. The structural, morphological and optical characterization techniques were applied to identify the physio-chemical properties of the prepared materials. Additionally, the superior performance of this n-p-n nanostructured material was demonstrated in the destruction of micro organic (chlorophenol) toxic wastes under visible light. The accomplished ability of the prepared catalysts (up to 92% degradation of chlorophenol after 180 min of irradiation) and their profound degradation mechanism was explained in detail.
The growing prevalence of new toxins in the environment continues to cause widespread concerns. Pharmaceuticals, organic pollutants, heavy metal ions, endocrine-disrupting substances, microorganisms, and others are examples of persistent organic chemicals whose effects are unknown because they have recently entered the environment and are displaying up in wastewater treatment facilities. Pharmaceutical pollutants in discharged wastewater have become a danger to animals, marine species, humans, and the environment. Although their presence in drinking water has generated significant concerns, little is known about their destiny and environmental effects. As a result, there is a rising need for selective, sensitive, quick, easy-to-handle, and low-cost early monitoring detection systems. This study aims to deliver an overview of a low-cost carbon-based composite to detect and remove pharmaceutical components from wastewater using the literature reviews and bibliometric analysis technique from 1970 to 2021 based on the web of science (WoS) database. Various pollutants in water and soil were reviewed, and different methods were introduced to detect pharmaceutical pollutants. The advantages and drawbacks of varying carbon-based materials for sensing and removing pharmaceutical wastes were also introduced. Finally, the available techniques for wastewater treatment, challenges and future perspectives on the recent progress were highlighted. The suggestions in this article will facilitate the development of novel on-site methods for removing emerging pollutants from pharmaceutical effluents and commercial enterprises.
Water contamination is an environmental burden for the next generations, calling for advanced methods such as adsorption to remove pollutants. For instance, unwanted biowaste and invasive plants can be converted into biosorbents for environmental remediation. This would partly solve the negative effects of invasive plants, estimated at 120 billion dollars in the USA. Here we review the distribution, impact, and use of invasive plants for water treatment, with emphasis on the preparation of biosorbents and removal of pollutants such as cadmium, lead, copper, zinc, nickel, mercury, chromate, synthetic dyes, and fossil fuels. Those biosorbents can remove 90-99% heavy metals from aqueous solutions. High adsorption capacities of 476.190 mg/g for synthetic dyes and 211 g/g for diesel oils have been observed. We also discuss the regeneration of these biosorbents.
Pollution and diseases such as the coronavirus pandemic (COVID-19) are major issues that may be solved partly by nanotechnology. Here we review the synthesis of ZrO2 nanoparticles and their nanocomposites using compounds from bacteria, fungi, microalgae, and plants. For instance, bacteria, microalgae, and fungi secret bioactive metabolites such as fucoidans, digestive enzymes, and proteins, while plant tissues are rich in reducing sugars, polyphenols, flavonoids, saponins, and amino acids. These compounds allow reducing, capping, chelating, and stabilizing during the transformation of Zr4+ into ZrO2 nanoparticles. Green ZrO2 nanoparticles display unique properties such as a nanoscale size of 5-50 nm, diverse morphologies, e.g. nanospheres, nanorods and nanochains, and wide bandgap energy of 3.7-5.5 eV. Their high stability and biocompatibility are suitable biomedical and environmental applications, such as pathogen and cancer inactivation, and pollutant removal. Emerging applications of green ZrO2-based nanocomposites include water treatment, catalytic reduction, nanoelectronic devices, and anti-biofilms.
The presence of microplastics (MP) and nanoplastics (NP) in the environment poses significant hazards towards microorganisms, humans, animals and plants. This paper is focused on recent literature studies and patents discussing the removal process of these plastic pollutants. Microplastics and nanoplastics can be quantified by counting, weighing, absorbance and turbidity and can be further analyzed using scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, surface-enhanced Raman spectroscopy and Raman tweezers. Mitigation methods reported are categorized depending on the removal characteristics: (i) Filtration and separation method: Filtration and separation, electrospun nanofiber membrane, constructed wetlands; (ii) Capture and surface attachment method: coagulation, flocculation and sedimentation (CFS), electrocoagulation, adsorption, magnetization, micromachines, superhydrophobic materials and microorganism aggregation; and (iii) Degradation method: photocatalytic degradation, microorganism degradation and thermal degradation; where removal efficiency between 58 and 100% were reported. As these methods are significantly distinctive, the parameters which affect the MP/NP removal performance e.g., pH, type of plastics, presence of interfering chemicals or ions, surface charges etc. are also discussed. 42 granted international patents related to microplastics and nanoplastics removal are also reviewed where the majority of these patents are focused on separation or filtration devices. These devices are efficient for microplastics up to 20 μm but may be ineffective for nanoplastics or fibrous plastics. Several patents were found to focus on methods similar to literature studies e.g., magnetization, CFS, biofilm and microorganism aggregation; with the addition of another method: thermal degradation.
Solvent-based recycling of plastic can offer the main improvement when it is employed for pyrolysis-catalytic steam reforming. In this research, plastic waste dissolved in phenol was used as a feed for catalytic cracking and steam reforming reactions for valuable liquid fuels and hydrogen production, which is gaining the attention of researchers globally. Microplastic wastes (MPWs) are tiny plastic particles that arise due to product creation and breakdown of larger plastics. They can be found mainly in several habitats, including seas and freshwater ecosystems. MPWs harm aquatic species, turtles, and birds and were chosen to recover in this study that can be reacted on the catalyst surface. Biphasic anatase-rutile TiO2 with spherical-shaped support for Ni and Pd metals with nanosized particles was synthesized via the hydrothermal treatment method, and its chemical and physical properties were characterized accordingly. According to temperature-programmed desorption of carbon dioxide (CO2-TPD) and temperature-programmed reduction of hydrogen (H2-TPR) results, the incorporation of Pd into Ni/TNPs enhanced the basicity of the support surface and the redox properties of catalysts, which were strongly linked to the improved hydrogen yield (71%) and phenol conversion (79%) at 600 °C. The Ni-Pd/TNPs nanocatalyst, with remarkable stability for 72 h of time on stream, is a promising catalyst for the MPW-phenol cracking and steam reforming reactions toward H2 production for clean energy generation and other environmental applications. Besides, this study has also highlighted the opportunities of overcoming the risk of microplastic waste and converting it into valuable fuels such as decamethyltetrasiloxane, phenanthrene, methyl palmitate, benzenepropanoic acid, benzoic acid, azulene, xanthene, anisole, biphenyl, phthalic acid, diisooctyl phthalate, etc.
Photocatalytic degradation is a valuable direction for eliminating organic pollutants in the environment because of its exceptional catalytic activity and low energy requirements. As one of the prospective photocatalysts, zirconium dioxide (ZrO2) is a promising candidate for photoactivity due to its favorable redox potential and higher chemical stability. ZrO2 has a high rate of electron-hole recombination and poor light-harvesting capabilities. Still, modification has demonstrated enhancements, especially extra-modification, and is therefore worthy of investigation. This present review provides a comprehensive overview of the extra-modifications of ZrO2 for enhanced photocatalytic performance, including coupling with other semiconductors, doping with metal, non-metal, and co-doping with metal and non-metal. The extra-modified ZrO2 showed superior performance in degrading the organic pollutant, particularly dyes and phenolic compounds. Interestingly, this review also briefly highlighted the probable mechanisms of the extra-modification of ZrO2 such as p-n heterojunction, type II heterojunction, and Z-scheme heterojunction. The latter heterojunction with excellent electron-hole space separation improved the photoactivity. Extensive research on ZrO2's photocatalytic potential is presented, including the removal of heavy metals, the redox of heavy metals and organic pollutants, and the evolution of hydrogen. Modified ZrO2's photocatalytic effectiveness depends on its band position, oxygen vacancy concentration, and metal defect sites. The opportunities and future problems of the extra-modified ZrO2 photocatalyst are also discussed. This review aims to share knowledge regarding extra-modified ZrO2 photocatalysts and inspire new environmental remediation applications.
The subject of water contamination and how it gets defiled to the society and humans is confabulating from the past decades. Phenolic compounds widely exist in the water sources and it is emergent to determine the toxicity in natural and drinking water, because it is hazardous to the humans. Among these compounds, catechol has sought a strong concern because of its rapid occurrence in nature and its potential toxicity to humans. The present work aims to develop an effective electrochemical sensing of catechol using mesoporous structure of Fe3O4-TiO2 decorated on glassy carbon (GC) electrode. The creation of pure TiO2 using the sol-gel technique was the first step in the synthesis protocol for binary nanocomposite, which was then followed by the loading of Fe3O4 nanoparticles on the surface of TiO2 using the thermal decomposition method. The resultant Fe3O4-TiO2 based nanocomposite exhibited mesoporous structure and the cavities were occupied with highly active magnetite nanoparticles (Fe3O4) with high specific surface area (90.63 m2/g). When compared to pure TiO2, catechol showed a more prominent electrochemical response for Fe3O4-TiO2, with a significant increase in anodic peak current at a lower oxidation potential (0.387 V) with a detection limit of 45 μM. Therefore, the prepared magnetite binary nanocomposite can serve as an efficient electroactive material for sensing of catechol, which could also act as a promising electrocatalyst for various electrocatalytic applications.
Microplastic (MP) is an emerging contaminant of concern due to its ubiquitous quantity in the environment, small size, and potential toxicity due to strong affinity towards other contaminants. In this work, MP particles (5-300 μm) were extracted from a commercial facial cleanser and determined to be irregular polyethylene (PE) microbeads based on characterization with field emission scanning electron microscopy (FESEM) and Raman spectroscopy. The potential of extracted MP acting as toxic pollutants' vector was analyzed via adsorption of methylene blue and methyl orange dye where significant dye uptake was observed. Synthetic wastewater containing the extracted MP was subjected to a continuous-flow column study using palm kernel shell and coconut shell biochar as the filter/adsorbent media. The prepared biochar was characterized via proximate and ultimate analysis, FESEM, contact angle measurement, atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy to investigate the role of the biochar properties in MP removal. MP removal performance was determined by measuring the turbidity and weighing the dry mass of particles remaining in the effluent following treatment. Promising results were obtained from the study with highest removal of MP (96.65%) attained through palm kernel shell biochar with particle size of 0.6-1.18 mm and continuous-flow column size of 20 mm.
Bidens pilosa is classified as an invasive plant and has become a problematic weed to many agricultural crops. This species strongly germinates, grows and reproduces and competing for nutrients with local plants. To lessen the influence of Bidens pilosa, therefore, converting this harmful species into carbon materials as adsorbents in harm-to-wealth and valorization strategies is required. Here, we synthesized a series of magnetic composites based on MFe2O4 (M = Ni, Co, Zn, Fe) supported on porous carbon (MFOAC) derived from Bidens pilosa by a facile hydrothermal method. The Bidens pilosa carbon was initially activated by condensed H3PO4 to increase the surface chemistry. We observed that porous carbon loaded NiFe2O4 (NFOAC) reached the highest surface area (795.7 m2 g-1), followed by CoFe2O4/AC (449.1 m2 g-1), Fe3O4/AC (426.1 m2 g-1), ZnFe2O4/AC (409.5 m2 g-1). Morphological results showed nanoparticles were well-dispersed on the surface of carbon. RhB, MO, and MR dyes were used as adsorbate to test the adsorption by MFOAC. Effect of time (0-360 min), concentration (5-50 mg L-1), dosage (0.05-0.2 g L-1), and pH (3-9) on dyes adsorption onto MFOAC was investigated. It was found that NFOAC obtained the highest maximum adsorption capacity against dyes, RhB (107.96 mg g-1)
Several activities such as aquaculture, human and feedstock therapies can directly release antibiotics into water. Due to high stability, low hydrolysis and non-biodegradation, they can accumulate in the aqueous environment and transport to aquatic species. Here, we synthesized amine-functionalized porous carbons (ANC) by a direct-pyrolysis process of NH2-MIL-53(Al) as a sacrificial template at between 600 and 900 °C and utilized them to eliminate chloramphenicol antibiotic from water. The NH2-MIL-53(Al)-derived porous carbons obtained high surface areas (304.7-1600 m2 g-1) and chloramphenicol adsorption capacities (148.3-261.5 mg g-1). Several factors such as hydrogen bonding, Yoshida hydrogen bonding, and π-π interaction, hydrophobic interaction possibly controlled adsorption mechanisms. The ANC800 could be reused four cycles along with high stability in structure. As a result, NH2-MIL-53(Al)-derived porous carbons are recommended as recyclable and efficient adsorbents to the treatment of antibiotics in water.
The worldwide demand for antibiotics has experienced a notable surge, propelled by the repercussions of the COVID-19 pandemic and advancements in the global healthcare sector. A prominent challenge confronting humanity is the unregulated release of antibiotic-laden wastewater into the environment, posing significant threats to public health. The adoption of affordable carbon-based adsorbents emerges as a promising strategy for mitigating the contamination of antibiotic wastewater. Here, we report the synthesis of novel porous carbons (MPC) through a direct pyrolysis of MIL-53-NH2(Al) and tannic acid (TANA) under N2 atmosphere at 800 °C for 4 h. The effect of TANA amount ratios (0%-20%, wt wt-1) on porous carbon structure and adsorption performance was investigated. Results showed that TANA modification resulted in decreased surface area (1,600 m2 g-1-949 m2 g-1) and pore volume (2.3 cm3 g-1-1.7 cm3 g-1), but supplied hydroxyl functional groups. Adsorption kinetic, intraparticle diffusion, and isotherm were examined, indicating the best fit of Elovich and Langmuir models. 10%-TANA-MPC obtained an ultrahigh adsorption capacity of 564.4 mg g-1, which was approximately 2.1 times higher than that of unmodified porous carbon. 10%-TANA-MPC could be easily recycled up to 5 times, and after reuse, this adsorbent still remained highly stable in morphology and surface area. The contribution of H bonding, pore-filling, electrostatic and π-π interactions to chloramphenicol adsorption was clarified. It is recommended that TANA-modified MIL-53-NH2(Al)-derived porous carbons act as a potential adsorbent for removal of pollutants effectively.
Carbon-integrated binary metal oxide semiconductors have gained prominence in the last decade as a better material for photocatalytic wastewater treatment technology. In this regard, this research describes the investigation of the binary metal oxide TiO2@Fe3O4 embedded on reduced graphene oxide (rGO) nanosheets synthesized through a combination of sol-gel, chemical precipitation, and Hummer's processes. Besides, the catalyst is applied for the photocatalytic degradation of organic chlorophenol pollutants. The characterized diffraction results showed the peak broadening of the rGO-TiO2@Fe3O4 composite formed with tetragonal and cubic structures having small crystallite sizes. The TEM observation shows an enormous miniature of TiO2@Fe3O4 nanospheres spread on the folded 2D-rGO nanosheets with a large BET surface area. The XPS result holds the mixed phases of Fe3O4 and Fe2O3. Finally, the catalyst demonstrated a low band gap with extended light absorption towards visible light irradiation. The synergistic interactions between Fe3+ and Fe2+ improved the visible light activity due to the incorporation of rGO, and also possessed good recycling capacity. The increased mobility of electrons at the interfaces of TiO2 and Fe3O4 due to the mixing of rGO results in the separation of charge carriers by elevating the photocatalytic degradation efficiency of chlorophenol.
AbstractIn this paper, the adsorption of the chlorinated organic compound, 2,4-dichlorophenol, using activated carbon (AC), bagasse fly ash (BFA) and rice husk fly ash (RHFA) in a packed bed column was simulated using Aspen Adsorption software. The purpose of this study was to demonstrate the effectiveness of simulation software for identifying alternative low-cost adsorbents and optimising the adsorption process. The effect of process parameters such as initial concentration, bed height and inlet feed flow rate were evaluated using breakthrough curves. It was shown that the longest breakthrough times were at a higher bed height of 3 m and lower flow rate of 2 m3/hr and concentration had no effect on breakthrough time. After optimisation using response surface methodology, the AC, BFA and RHFA had a breakthrough time of 534 s, 426 s and 209 s, respectively. This shows the potential of BFA as a potential alternative for AC for the adsorption of 2,4-dichlorophenol and shows RHFA to be a relatively poor adsorbent in comparison. The economic evaluation illustrates that the overall cost of wastewater treatment with BFA and RHFA is lower than AC. The cost for the BFA and RHFA adsorbents is only a handling charge, but the cost for using AC adsorbent is £10,603/year. Therefore, the company can produce 17,520 m3/year of fresh water from the adsorbent and save £87,600/year. Therefore, it was concluded that BFA had a slightly weaker adsorption efficiency than AC but was more cost effective, allowing it to be more affordable and increasing its availability.
To consider silver nanoparticles (AgNPs) as a colorimetric sensor for H2O2 we require investigation of the effects of the homogeneity of the nanoparticle size and morphology on the sensor parameters. Uniformly-sized Ag nanoparticles with diameters of ∼18.8 ± 2.8 nm were produced using microwave irradiation (AgNP1) but non-uniform particles with diameters of ∼71.2 ± 19.4 nm (AgNP2) were formed without microwave irradiation. Microwave synthesis produced AgNP1 with superiority in terms of repeatability, selectivity and sensor stability for up to eight months of storage over AgNP2. AgNP1 exhibited higher sensitivity and detection limits in the working range of 0.01-40000 μM as compared to AgNP2. The application of the AgNP sensor to milk samples provided recovery values of 99.09-100.56% for AgNP1 and 98.18-101.90% for AgNP2. Microwave irradiation resulted in strong and uniform PVP-Ag interactions for isotropic growth into small nanoparticles. Size and morphology uniformity determined the characteristics of the AgNP sensor that can be applied for H2O2 detection in a wide range of concentrations and real-time evaluation, with the potential for industrial applications.