ABSTRACT
Per- and polyfluoroalkyl substances (PFAS) are oxidatively recalcitrant organic synthetic compounds. PFAS are an exceptional group of chemicals that have significant physical characteristics due to the presence of the most electronegative element (i.e., fluorine). PFAS persist in the environment, bioaccumulate, and have been linked to toxicological impacts. Epidemiological and toxicity studies have shown that PFAS pose environmental and health risks, requiring their complete elimination from the environment. Various separation technologies, including adsorption with activated carbon or ion exchange resin; nanofiltration; reverse osmosis; and destruction methods (e.g., sonolysis, thermally induced reduction, and photocatalytic dissociation) have been evaluated to remove PFAS from drinking water supplies. In this review, we will comprehensively summarize previous reports on the photodegradation of PFAS with a special focus on photocatalysis. Additionally, challenges associated with these approaches along with perspectives on the state-of-the-art approaches will be discussed. Finally, the photocatalytic defluorination mechanism of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) following complete mineralization will also be examined in detail.
ABSTRACT
Per- and polyfluoroalkyl substances (PFAS) are a set of synthetic chemicals which contain several carbon-fluorine (C-F) bonds and have been in production for the past eight decades. PFAS have been used in several industrial and consumer products including nonstick pans, food packaging, firefighting foams, and carpeting. PFAS require proper investigations worldwide due to their omnipresence in the biotic environment and the resulting pollution to drinking water sources. These harmful chemicals have been associated with adverse health effects such as liver damage, cancer, low fertility, hormone subjugation, and thyroid illness. In addition, these fluorinated compounds show high chemical, thermal, biological, hydrolytic, photochemical, and oxidative stability. Therefore, effective treatment processes are required for the removal and degradation of PFAS from wastewater, drinking water, and groundwater. Previous review papers have provided excellent summaries on PFAS treatment technologies, but the focus has been on the elimination efficiency without providing mechanistic understanding of removal/degradation pathways. The present review summarizes a comprehensive examination of various thermal and non-thermal PFAS destruction technologies. It includes sonochemical/ultrasound degradation, microwave hydrothermal treatment, subcritical or supercritical treatment, electrical discharge plasma technology, thermal destruction methods/incinerations, low/high-temperature thermal desorption process, vapor energy generator (VEG) technology and mechanochemical destruction. The background, degradation mechanisms/pathways, and advances of each remediation process are discussed in detail in this review.
ABSTRACT
Per- and polyfluoroalkyl substances (PFAS) are synthetic organic molecules used to manufacture various consumer and industrials products. In PFAS, the CF bond is stable, which renders these compounds chemically stable and prevents their breakdown. Several PFAS treatment processes such as adsorption, photolysis and photocatalysis, bioremediation, sonolysis, electrochemical oxidation, etc., have been explored and are being developed. The present review article has critically summarized degradative technologies and provides in-depth knowledge of photodegradation, electrochemical degradation, chemical oxidation, and reduction mineralization mechanism. Also, novel non-degradative technologies, including nano-adsorbents, natural and surface-modified clay minerals/zeolites, calixarene-based polymers, and molecularly imprinted polymers and adsorbents derived from biomaterials are discussed in detail. Of these novel approaches photocatalysis combined with membrane filtration or electrochemical oxidation via a treatment train approach shows promising results in removing PFAS in natural waters. The photocatalytic mineralization mechanism of PFOA is discussed, leading to recommendations for future research on novel remediation strategies for removing PFAS from water.
Subject(s)
Fluorocarbons , Water Pollutants, Chemical , Adsorption , Clay , Fluorocarbons/analysis , Water , Water Pollutants, Chemical/analysisABSTRACT
Per- and polyfluoroalkyl substances (PFAS) are a large group of perfluorinated organic molecules that have been in use since the 1940s for industrial, commercial, and consumer applications. PFAS are a growing concern because some of them have shown persistent, bioaccumulative and toxic effects. Herein, we demonstrate an innovative technology of UV-vis/ZnxCu1-xFe2O4/oxalic acid for the degradation of perfluorooctanoic acid (PFOA) in water. The magnetically retrievable nanocrystalline heterogeneous ferrite catalysts, ZnxCu1-xFe2O4 were synthesized using a sol-gel auto-combustion process followed by calcination at 400 °C. The combination of ZnxCu1-xFe2O4 and oxalic acid generate reactive species under UV light irradiation. These reactive species are then shown to be capable of the photodegradation of PFOA. The degree of degradation is tracked by identifying transformation products using liquid chromatography coupled with quadrupole time-of-flight mass spectroscopy (LC-QTOF-MS).
Subject(s)
Fluorocarbons , Caprylates , Oxalic Acid , Technology , Ultraviolet Rays , ZincABSTRACT
A variety of methods, including chemical precipitation, biological phosphorus elimination, and adsorption, have been described to effectively eliminate phosphorus (P) in the form of phosphate (PO4 3-) from wastewater sources. Adsorption is a simple and easy method. It shows excellent removal performance, cost effectiveness, and the substantial option of adsorbent materials. Therefore, it has been recognized as a practical, environmentally friendly, and reliable treatment method for eliminating P. Nanocomposites have been deployed to remove P from wastewater via adsorption. Nanocomposites offer low-temperature alteration, high specific surface area, adjustable surface chemistry, pore size, many adsorption sites, and rapid intraparticle diffusion distances. In this Mini-Review, we have aimed to summarize the last eight years of progress in P removal using graphene-based composites via adsorption. Ultimately, future perspectives have been presented to boost the progress of this encouraging field.
ABSTRACT
Goethite with protuberant lychee morphology has been synthesized that accomplishes C-H activation of N-methylanilines to generate α-aminonitriles; the catalyst takes oxygen from air and uses it as a co-oxidant in the process.
ABSTRACT
Graphitic carbon nitride supported palladium nanoparticles, Pd@g-C3N4, have been synthesized and utilized for the direct oxidative esterification of alcohols using atmospheric oxygen as a co-oxidant via photocatalytic C-H activation.
ABSTRACT
An efficient continuous flow protocol has been developed for bond C-H activation which promotes the α-cyanation of secondary and tertiary amines using magnetic nano-ferrites.
ABSTRACT
Chitosan-derived, porous nitrogen-enriched carbonaceous carbon nitride catalyst (PCNx) has been synthesized from marine waste and its use demonstrated in a metal-free heterogeneous selective oxidation of 5-hydroxymethyl-furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) using aerial oxygen under mild reaction conditions.
ABSTRACT
A titanium-based zeolitic thiophene-benzimidazolate framework has been designed for the direct synthesis of dimethyl carbonate (DMC) from methanol and carbon dioxide. The developed catalyst activates carbon dioxide and delivers over 16% yield of DMC without the use of any dehydrating agent or requirement for azeotropic distillation.
ABSTRACT
Bimetallic CuAg@g-C3N4 catalyst system has been designed and synthesized by impregnating copper and silver nanoparticles over the graphitic carbon nitride surface. Its application has been demonstrated in the hydroxylation of benzene under visible light.
ABSTRACT
The titanium cluster with the reduced band gap has been synthesized having the palladium nanoparticles over the surface, which not only binds to the atmospheric oxygen but also catalyzes the oxidation of alcohols under visible light.
ABSTRACT
An organic sulfonated graphitic carbon nitride is synthesized and its application has been demonstrated in the conversion of carbohydrates into furanics and related value-added products. The most important feature of the material is the stability and acidity, which could be utilized at elevated temperatures for cleaving carbohydrates and converting them into biologically important scaffolds and platform chemicals.
ABSTRACT
An efficient and direct oxidation of aromatic amines to aromatic azo-compounds has been achieved using a MnO2@g- C3N4 catalyst under visible light as a source of energy at room temperature.
ABSTRACT
Sulfonation of graphitic carbon nitride (g-CN) affords a polar and strongly acidic catalyst, Sg-CN, which displays unprecedented reactivity and selectivity in biodiesel synthesis and esterification reactions at room temperature.
ABSTRACT
Magnetic graphitic carbon nitride, Fe@g-C3N4, has been synthesized by adorning a graphitic carbon nitride (g-C3N4) support with iron oxide via non-covalent interaction. The magnetically recyclable catalyst showed excellent reactivity for the expeditious C-H activation and cyanation of amines.
Subject(s)
Amines/chemistry , Iron/chemistry , Nitriles/chemical synthesis , Catalysis , Magnetic Phenomena , Molecular Structure , Nitriles/chemistryABSTRACT
Nanocrystalline starch produced from the acid hydrolysis of gelatinized starch has been used for the first time to support palladium(II) ethylenediamine complex. The nanocrystalline starch supported Pd(II) complex was found to be an efficient and efficiently recycled catalyst for the Mizoroki-Heck reaction of furans and thiophenes with styrenes under mild reaction conditions.
Subject(s)
Furans/chemistry , Nanoparticles/chemistry , Organometallic Compounds/chemistry , Palladium/chemistry , Starch/chemistry , Thiophenes/chemistry , Catalysis , Ethylenediamines/chemistry , Molecular Structure , Organometallic Compounds/chemical synthesis , Styrenes/chemistryABSTRACT
Highly dispersed Pd-nanoparticles grafted onto amino-functionalized nanocrystalline starch were found to be excellent heterogeneous catalysts for the aerobic oxidation of a variety of alcohols to their corresponding carbonyl compounds in excellent yields. The prepared catalyst was found to be selective for the oxidation of primary alcohols to aldehydes without giving over-oxidation products and was recycled several times without any leaching of the metal into the solution.
Subject(s)
Alcohols/chemistry , Metal Nanoparticles/chemistry , Oxidants/chemistry , Palladium/chemistry , Starch/chemistry , Catalysis , Oxidation-ReductionABSTRACT
Well-dispersed iron nanoparticles supported on chemically derived graphene oxide containing uniform distribution of iron nanoparticles (FeNPs) throughout the surface was synthesized and was used as a heterogeneous catalyst for oxidative cyanation of tertiary amines to the corresponding α-aminonitriles in high to excellent yields using hydrogen peroxide with sodium cyanide in acetic acid. After the reaction the catalyst could easily be separated by the influence of an external magnet and reused for several runs without any significant change in the catalytic activity and without leaching of the metal during the reaction.
