Pyrolysis Time Research Articles

The initiation stage of thermochemical sulfate reduction: An isotopic and computational study

Thermochemical sulfate reduction (TSR) is one of the most important organic-inorganic reactions in petroleum reservoirs which significantly affects production and processing risks. The initiation (non-catalyzed) stage of TSR is critical in constructing a reliable kinetic model to predict this reaction. There is a large gap in our understanding of the mechanisms involved in this stage. In the present study, we used hydrous pyrolysis experiments with Na2SO4 and 1-dodecene as model compounds at pH= 1, and temperatures of 250 °C and 300 °C to simulate this early TSR stage. We measured and calculated the sulfur isotopic fractionations of sulfate, H2S and individual organic sulfur compounds (OSC). A thermodynamic model was used to determine the concentrations of the different sulfate species (H2SO4, HSO4¯, SO42-) at the experimental conditions. We then used ab initio calculations to determine possible radical and non-radical reaction mechanisms to explain the experimental results. During all the experiments, sulfate was consumed gradually while H2S and OSC were produced. The residual sulfate was 34S enriched up to 10.7‰ relative to the initial sulfate as pyrolysis time advanced. The produced H2S and OSC were typically about 21‰ 34S depleted relative to co-existing sulfate. The formation of OSC, such as C24 sulfides and C12 thiophenes, during the experiments and their similar δ34S values, suggest a common precursor and that radical mechanisms are involved in their formation. Calculated activation energies and free energies (Ea and ∆G‡, respectively) for the radical TSR mechanisms (20.6–34.1 and 32.3–44.4 kcal mol−1, respectively) yielded lower values than the non-radical TSR mechanisms (53.5–68.5 and 59.7–78.1 kcal mol−1, respectively). However, the calculated kinetic fractionation factors for the non-radical mechanism correlated better with the 11–12‰ experimental fractionation factor of current and previous studies. This similarity between the experimental and computational results indicates that these non-radical rather than radical mechanisms were likely involved in the reduction of sulfate in our experiments. Despite the lower activation energies, the radical TSR mechanisms are not dominant in our experimental system, probably due to competing reactions of the active radical species (alkyl and allyl radicals). Nevertheless, under natural conditions, the significantly lower amount of alkenes is expected to reduce the competition on the active alkyl and allyl radicals for alkylation, making these radical mechanisms competing pathways for the initiation stage of TSR.

Comparison of non-catalytic and in-situ catalytic pyrolysis of Melia azedarach sawdust

This study focused on the in-situ catalytic pyrolysis of Melia azedarach sawdust by impregnating it with copper (Cu). Native and Cu impregnated Melia azedarach sawdust (MAS-N and MAS-C, respectively) were subjected to pyrolysis. MAS-N and MAS-C were characterized using proximate, ultimate and HHV analysis. Thermal degradation performance of MAS-N and MAS-C were examined by thermogravimetric analysis. Similar shapes of thermogravimetric curves indicated that Cu metal did not alter degradation pathway but lowered decomposition temperature and higher reaction rates were noticed for MAS-C due to catalytic effect of Cu. Optimization of operating process parameters was done by varying temperature, sweeping gas flow rate, particle size, packed bed height, pyrolysis time and heating rate for MAS-N. Maximum bio-oil yield for MAS-N was obtained at 550 ℃ temperature, 150 mL/min nitrogen flow rate, 8.4 cm bed height, 0.18–0.29 mm sized particles, 20 ℃/min heating rate and 60 min pyrolysis time. Further, effect of variation in temperature and catalyst to biomass ratio was studied for MAS-C and maximum bio-oil yield for MAS-C was obtained at lower temperature than that for MAS-N. Results were compared for catalytic and non-catalytic pyrolysis products via various characterization methods. Bio-oil properties were analysed by FTIR, GC-MS and 13C NMR. Proximate, ultimate, HHV, FTIR, XRD, SEM and BET surface area analysis were used to characterize properties of bio-char. Results suggested that Cu has catalytic effect on pyrolysis products. This article will be useful for promoting future research related to using heavy metal contaminated biomass as potential opportunities.

Carbon superstructure nanoflower derived from self-assembly of polyimide for superior lithium storage

In this paper, three-dimensional carbon superstructures (CSSs) have been proposed through an effective method. Specifically, the hierarchical self-assembly of polyimide (PI) is followed by thermal annealing. Moreover, the structural evolution of PI under the various pyrolysis time was also comprehensively studied. It is noted that the as-prepared CSSs as anode composites for LIBs, especially CSS-5 h, exhibited extraordinary electrochemical properties, exhibiting a high reversible performance, great rate performance, and excellent cycling stability. As expected, the superior electrochemical capability can be ascribed to the synergistic effect of combining the nanoflower-like carbon superstructures with nitrogen contents. Such a method might encourage the inspirations to devise and obtain various heteroatom-modulated and hierarchical polymer-derived carbon composites for LIBs.

Efficient Treatment of Oily Sludge via Fast Microwave-Assisted Pyrolysis, Followed by Thermal Plasma Vitrification.

Oily sludge, as a critical hazardous waste, requires appropriate treatment for resource recovery and harmfulness reduction. Here, fast microwave-assisted pyrolysis (MAP) of oily sludge was conducted for oil removal and fuel production. The results indicated the priority of the fast MAP compared with the MAP under premixing mode, with the oil content in solid residues after pyrolysis reaching below 0.2%. The effects of pyrolysis temperature and time on product distribution and compositions were examined. In addition, pyrolysis kinetics can be well described using the Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) methods, with the activation energy being 169.7-319.1 kJ/mol in the feedstock conversional fraction range of 0.2-0.7. Subsequently, the pyrolysis residues were further treated by thermal plasma vitrification to immobilize the existing heavy metals. The amorphous phase and the glassy matrix were formed in the molten slags, resulting in bonding and, hence, immobilization of heavy metals. Operating parameters, including working current and melting time, were optimized to reduce the leaching concentrations of heavy metals, as well as to decrease their volatilization during vitrification.

Microwave Assisted Pyrolysis of Moringa Seed and Karanja for Bio-Oil Production

Microwave-assisted pyrolysis is an alternative technique of conventional heating which undergo thermochemical process to convert biomass to bio oil, bio char and biogas. Microwave-assisted pyrolysis is more rapid and efficient to produce product compared to conventional heating. A modified household microwave oven with 800W was used to pyrolyze Moringa seed and Karanja to become bio oil and bio char. This experiment was repeated in different parameters such as time, temperature and power to obtain maximum bio oil yield. Bio oil yield of Moringa seed increased from 7.2 wt% at 300°C in 5 minutes to 10.6 wt% at 450°C in 13 minutes. Bio oil of both raw materials showed maximum yield when pyrolysis time is 13 minutes in 800W but after 13 minutes, the bio oil yield of Moringa decrease of 2.4% and bio oil yield of Karanja decrease of 4.7%. The calorific value of Moringa bio oil is 25.08MJ/kg whereas Karanja bio oil is 20.36 MJ/kg. Functional group of both bio oil mainly include alcohol, ketones, aldehydes and carboxylic acid. The pH value of Moringa bio oil and Karanja bio oil are 4.38 and 5.86 respectively.

In-situ hydrogen peroxide formation and persulfate activation over banana peel-derived biochar cathode for electrochemical water treatment in a flow reactor

Electrochemical advanced oxidation processes (EAOPs) are effective for the removal of organic contaminants from groundwater. The choice of an affordable cathode material that can generate reactive oxygen species (ROS) such as hydrogen peroxide (H2O2) and hydroxyl radicals (•OH) will increase practicality and cost effectiveness of EAOPs. Carbon enriched biochar (BC), which is derived from pyrolysis of biomass, has emerged as an inexpensive and environmentally-friendly electrocatalyst for removing contaminants from groundwater. In this study, a banana peel-derived biochar (BP-BC) cathode packed in a stainless steel (SS) mesh was used in a continuous flow reactor to degrade the ibuprofen (IBP), as a model contaminant. The BP-BC cathodes generate H2O2 via a 2-electron oxygen reduction reaction, initiate the H2O2 decomposition to generate •OH, adsorb IBP from contaminated water, and oxidize IBP by formed •OH. Various reaction parameters such as pyrolysis temperature and time, BP mass, current, and flow rate, were optimized to maximize IBP removal. Initial experiments showed that H2O2 generation was limited (∼3.4 mg mL−1), resulting in only ∼ 40% IBP degradation, due to insufficient surface functionalities on the BP-BC surface. The addition of persulfate (PS) into the continuous flow system significantly improves the IBP removal efficiency via PS activation. The in-situ H2O2 formation and PS activation over BP-BC cathode results in concurrent generation of •OH and sulfate anion radicals (SO4•−, a reactive oxidant), respectively, which collectively achieve ∼ 100% IBP degradation. Further experiments with methanol and tertiary butanol as potential scavengers for •OH and SO4•− confirm their combined role in complete IBP degradation.

Study on the co-pyrolysis behaviors of sewage sludge and Enteromorpha prolifera and the adsorption mechanism of Cr(VI) in water using pyrolysis residue

The thermal–chemical conversion method has significant potential for the recovery of organic matter present in sewage sludge (abbreviated as SS), offering broad market prospects. In this study, a novel approach is proposed for the preparation of a composite adsorbent, named SS-EP, derived from the co-pyrolysis residue of sewage sludge and Enteromorpha prolifera. An orthogonal experiment was designed to investigate the performance of the adsorbent, and the results revealed that the optimal conditions were achieved when the SS proportion was 40%, the concentration of zinc chloride was 0.1 mol/l, the pyrolysis temperature was 500 °C, and the pyrolysis time was 30 min. Notably, the SS-EP composite adsorbent exhibited pronounced efficacy in the removal of Cr(VI) under both acidic and neutral conditions, achieving a removal rate exceeding 97%. Furthermore, the concentration of heavy metals in the leaching solution of the adsorbent was found to be significantly lower than the limit specified in the GB5085.3-2007 standard. Regeneration experiments demonstrated that even after the third regeneration, the SS-EP composite adsorbent maintained a removal rate of 70% for Cr(VI).

Recovery of carbon fibers from carbon fiber-reinforced epoxy-isophorone diamine composites via step thermolysis

Thermosetting composites are widely used in various industries owing to their excellent mechanical properties, dimensional stability, and convenient formability. However, once cured with epoxy resin, the separation of thermosetting composites from carbon fibers is challenging. Industrial waste resulting from end-of-service-life carbon fiber-reinforced thermosetting plastic (CFRP) is a significant environmental problem. Thus, eco-friendly and economic processes must be developed to increase resource efficiency by converting waste CFRP into reusable materials. This study aims to find the optimal conditions for the recovery of recycled carbon fiber (r-CF) from thermoset CFRP manufactured using epoxy (EP) and isophorone diamine (IPDA). A multi-step thermolysis method using superheated steam and air was proposed. We confirmed that an oxidizing atmosphere is required to recover clean r-CF without char. The mechanical strength of the recovered r-CF was dependent on the pyrolysis temperature and time, which was due to an increase in defects from the oxidative decomposition of the r-CF surface. Finally, the recovery rate was 95%, and the tensile strength of the recycled carbon fiber was 80% higher than that of virgin carbon fiber.

Pyrolysis behaviors of biomass tar-related model compounds catalyzed by Ni-modified HZSM-5 molecular sieve

To study the pyrolysis process and path of biomass tar, this paper took toluene as the biomass tar model compound, elected Ni-modified HZSM-5 molecular sieve as the catalyst, and established the catalytic pyrolysis process of toluene. By optimizing the process conditions of HZSM-5 catalyst modification and catalytic pyrolysis process of toluene, and comprehensively considering the indicators of catalyzing pyrolysis of toluene as biomass tar model compound, the pyrolysis behavior of aromatic tar model compounds catalyzed by Ni-modified HZSM-5 catalyst was deeply analyzed. Finally, the stability of the Ni-modified HZSM-5 catalyst was investigated with a pyrolysis time of 8 h. The best process conditions of Ni-modified HZSM-5 catalyst were obtained: SiO2/Al2O3 of 25, Ni loading of 8 wt%, and pyrolysis temperature of 700 ℃. The catalytic pyrolysis path of toluene as biomass tar model compound was clarified for the cracking and reforming of toluene for gas production, condensation and reforming reaction of liquid phase, and action of carbon deposition. The Ni-modified HZSM-5 molecular sieve shows excellent catalytic properties and application prospects, providing theoretical reference and data support for further designing and enhancing the structure of such catalysts and promoting tar removal efficiency.

Microwave-assisted In-situ catalytic co-pyrolysis of polypropylene and polystyrene mixtures: Response surface methodology analysis using machine learning

Polypropylene (PP) and Polystyrene (PS) are the major plastic fractions found in mixed plastic waste. Hence, the current study was focused to convert PP and PS into useful products via microwave-assisted pyrolysis (MAP). In addition, the understanding of feedstock conversion, product yields, and energy requirements in pyrolysis, co-pyrolysis, and catalytic co-pyrolysis was investigated. Experiments were conducted at a constant microwave power of 450 W till the reaction temperature reached up to 600 °C. When PS pyrolyzed, a heating rate of 56 °C/min resulted in 80 wt% of oil yield. Whereas PP pyrolysis produced 42 wt% of oil at a heating rate of 76 °C/min. In the PP: PS co-pyrolysis, the heating rate was decreased to 52 °C/min by yielding 51 wt% of oil. In catalytic co-pyrolysis of PP: PS with KOH resulted in variation in product yields and heating rate. An increase in PS quantity at a constant mass of PP resulted in the enhancement of oil yields from 58 to 84 wt% and a decrease in gas yields. The specific microwave power in the catalytic co-pyrolysis (7–18 W/g) is lower compared to the non-catalytic case (22–30 W/g). Whereas, the pyrolysis time in non-catalytic pyrolysis (7–11 min) is lower compared to catalytic co-pyrolysis (14–37 min). The addition of a catalyst resulted in a decrease (23–50%) in microwave conversion efficiency than that of the non-catalytic case (60–85%). The difference in predicted and actual result analysis proved co-pyrolysis synergy in product formation and energy consumption.

Study on synergistic pyrolysis and kinetics of mixed plastics based on spent fluid-catalytic-cracking catalyst

At present, disposable plastic products such as plastic packaging are very common in our daily life. These products are extremely easy to cause serious damage to the soil and marine environment due to their short design and service life, difficulties in degradation, or long degradation cycles. Thermochemical method (pyrolysis or catalytic pyrolysis) is an efficient and environmentally friendly way to treat plastic waste. In order to further reduce the energy consumption of plastic pyrolysis and improve the recycling rate of spent fluid catalytic cracking (FCC) catalysts, we adopt the "waste-to-waste" approach to apply the spent FCC catalysts as catalysts in the catalytic pyrolysis of plastics, exploring the pyrolysis characteristics, kinetic parameters, and synergistic effects between different typical plastics (polypropylene, low-density polyethylene, polystyrene). The experimental results show that the spent FCC catalysts used in the catalytic pyrolysis of plastics are beneficial to reduce the overall pyrolysis temperature and activation energy, in which the maximum weight loss temperature decreases by about 12℃ and the activation energy decreases by about 13%. The activity of spent FCC catalysts is improved after modification by microwave and ultrasonic, which further improve the catalytic efficiency and reduce the energy consumption of pyrolysis. The co-pyrolysis of mixed plastics is dominated by positive synergistic effect, which is conducive to improving the thermal degradation rate and shortening the pyrolysis time. This study provides relevant theoretical support for the resource application of spent FCC catalysts and "waste-to-waste" treatment of plastic waste.

Dolomite catalyst for fast pyrolysis of waste cooking oil into hydrocarbon fuel

Dolomite as the catalyst for pyrolysis of waste cooking oil (WCO) was investigated to produce hydrocarbon fuels. Optimization of pyrolysis parameters i.e. time, temperature and catalysts loading, achieved high selectivity of WCO to diesel hydrocarbon, compared to thermal pyrolysis that produced mainly carboxylic acids. Dolomite catalysed deoxygenation of fatty acid in WCO into hydrocarbon, consequently accelerating the pyrolysis time to 75 min. Bio-oil at 68.06% yield with 57.27% selectivity towards diesel and gasoline hydrocarbons was obtained at 450 °C while using 6% of dolomite. Dolomite exhibited partial phase separation into dolomite/CaCO3 mixtures within 15 min of pyrolysis, initiated by the generated CO2 during pyrolisis of WCO. The catalyst is stable for up to three reaction cycles suggesting the activity was achieved from the synergy between the dolomite/CaCO3 phases.

Study on the recycling of waste wind turbine blades

The pyrolysis process of waste wind turbine blades in the coal-fired flue gas was studied. The effects of pyrolysis temperature, pyrolysis time, flue gas composition and heating mode on the pyrolysis product were investigated, and the pyrolysis mechanism was also analyzed. Finally, the industrial implementation scheme of pyrolysis process in coal-fired power plants was formulated. The results showed that the matrix resin of wind turbine blades could be carbonized and then oxidized by direct heating with the flue gas. A clean glass fiber was finally obtained to recycle. When the blade was pyrolyzed at 420–450 ℃ for 5–6 h, the purity of recycled fiber was above 99 % and its tensile strength decrease was less than 10 % compared with the original fiber. During the pyrolysis process, the concentration of SO2 in flue gas had little effect on the quality of recycled fiber because of its nonreactivity with SiO2. With the increase of pyrolysis temperature, the purity of recycled fiber increased while its tensile strength decreased. In coal-fired power plants, a small fraction of flue gas was pumped from the tail flue of boiler by a fan. The flue gas after dust removal was sent to a recovery furnace, where the blade was pyrolyzed. The tail gas was transported to the boiler furnace for complete combustion and then purified by the existing pollutant purification devices in the power plant. According to the above scheme, the recycling of waste wind turbine blades in coal-fired power plants could be readily realized by equipping a duster, a recovery furnace and a fan.

Pyrolysis recycling of pig manure biochar adsorption material for decreasing ammonia nitrogen in biogas slurry

Biochar adsorption materials have a good removal effect on ammonia nitrogen in piggery biogas slurry. However, the cost of biochar adsorption material is still high. If these materials can be recycled several times, the cost can be significantly reduced. Therefore, this paper investigated a new process of biochar adsorption material (C@Mg-P) pyrolysis cycle for reducing ammonia nitrogen in piggery biogas slurry. The effects of pyrolysis process conditions (pyrolysis temperature and pyrolysis time) and number of recycling times on reducing ammonia nitrogen in biogas slurry by C@Mg-P were studied, a preliminary investigation on the reaction mechanism of C@Mg-P for reducing ammonia nitrogen in biogas slurry was conducted, and the economic feasibility of the pyrolysis recycling process was analyzed. It was found that the NH3-N elimination efficiency by C@Mg-P was 79.16 % under the optimal conditions of 0.5 h and 100 °C. Second, C@Mg-P removed 70.31 % NH3-N after recycling 10 times. Chemical precipitation, ion exchange, physical adsorption and electrostatic attraction were the potential reaction mechanisms for NH3-N reduction by C@Mg-P. Moreover, C@Mg-P had a good decolorization effect on piggery biogas slurry with a 72.56 % decolorization rate. Compared with the non-pyrolyzed recycling process, the proposed process saved 80 % of the cost, thus representing an economically possible approach for pig manure biochar application in wastewater denitrification treatment.

Utilizing 3-aminophenol formaldehyde resins microspheres for the synthesis of three-dimensionally ordered macroporous oxides

Constructing three-dimensionally ordered macroporous (3DOM) materials with well-defined structures and fascinating properties has attracted extensive attention in broad research fields. Innovations and breakthroughs are, thus, highly required for the control synthesis. Herein, we have successfully developed a novel strategy with 3-aminophenol formaldehyde resins microspheres as a template for the control synthesis of 3DOM TiO2. The as-prepared 3DOM TiO2 materials exhibit a periodic and interconnected macroporous structure with a large, well-open surface area of up to 208 m2/g. By rationally controlling the synthesis parameters, e.g. modulating the microsphere size of aminophenol formaldehyde resinsand the pyrolysis time, the average macroporous size of 3DOM TiO2 can be tunable in the range of 77–177 nm together with adjustable crystallinity of TiO2 obtained, and a different extent of the carbon residue decorated inside the macroporous can be also controlled. Given its generality and efficiency, we hope that the provided method can be a practical, economical viable approach for the rational design of various 3DOM materials, which provide great potentials for different application, including various aspects of catalysis and beyond.

Study of the Рossibility of Using Waste from the Agro-Industrial Complex and the Woodworking Industry in Order to Obtain High-Energy Fuel and Carbon Adsorbents

Growing concerns about the environment are prompting the search for alternative energy sources and the possibility of processing agricultural waste into highly efficient absorbents. That is why the article considers methods for obtaining high-energy fuel from pinewood using acidic additives and the possibility of using chemically treated cherry stone shells as a carbon sorbent is evaluated. With the use of low-temperature pyrolysis, a number of carbon-containing materials have been obtained. The carbon content in these materials depends on the reagent used to treat the feedstock, the temperature and time of pyrolysis. The subsequent activation of carbonizate from the cherry stone shell with oxidizing agents revealed that nitric acid significantly increases the cation-exchange capacity of the material, which allows it to be used as an adsorbent.

Carbon catalyst from palm kernel shell (PKS) for methane cracking: Effect of preparation

The effect of preparation on the performance of carbon catalyst derived from palm kernel shell (PKS) in methane cracking was evaluated. The PKS-carbon catalysts were prepared via pyrolysis at different temperatures (550, 650, 750 °C) and for different pyrolysis times (30, 60, 100 min) and their catalytic performance in methane cracking was analysed in a fixed bed reactor. The BET surface area of the PKS-carbon catalyst increased from 40.7 to 43.0 m2/g as the pyrolysis temperature increased from 550 to 650 °C, but decreased to 24.1 m2/g at 750 °C. During methane cracking, the PKS-carbon catalyst prepared at 650 °C demonstrated 30 % initial CH4 conversion and gave the highest initial H2 yield of up to 88 %. This indicates that pyrolysis temperature influences the carbon catalyst’s surface area, and a higher surface area promotes better initial catalytic activity in methane cracking. In addition, the PKS-carbon catalyst prepared for longer pyrolysis time (100 min) contained more desirable surface oxygen-containing functional groups (–OH, C=O, –COOH) than the ones prepared for 30 and 60 min. Therefore, the PKS-carbon catalyst pyrolyzed for 100 min exhibited 35 % initial CH4 conversion and the highest initial H2 yield of 95 %. This suggests that a longer pyrolysis time produces more desirable surface oxygen-containing functional groups, which enhance reactant activation in methane cracking. In conclusion, the preparation of PKS-carbon catalyst influences the surface area and surface oxygen- containing functional groups, which affect the catalyst’s performance in methane cracking.

Pengaruh Suhu dan Waktu Pirolisis terhadap Karakteristik Arang dari Tempurung Kelapa

The increased production of coconut has increased by the shell produced, even though this coconut shell has lignin content of 33.30% so it has the potential to be converted into charcoal through the pyrolysis process. Pyrolysis is a thermal decomposition process that occurs without air or with little air to convert biomass into charcoal. Coconut shell charcoal can be used for coal co-firing in developing new and renewable energy. This study aimed to obtain the best pyrolysis temperature and time in the manufacture of high-calorific value coconut shell charcoal in accordance with SNI 06-4369-1996. Coconut shell pyrolysis was carried out at temperatures of 350 °C, 450 °C and 550 °C and pyrolysis times of 2 hours, 3 hours and 4 hours. The results showed that charcoal with the highest calorific value was produced at a temperature of 450 °C and a pyrolysis time of 3 hours. The resulting charcoal had calorific value of 7,750.96 cal/g, yield of 30.10%, and contained 2.75% water, 2.70% ash and 9.50% volatile matter.

Determinations of Cadmium, Tin, Copper, Iron and Zinc in Food Samples by Electrothermal and Flame Atomic Absorption Spectrometries

Cadmium, tin, iron, copper, and zinc in tea, rice, and liver samples, and standard reference materials (IRMM 804 Rice Flour, GBW 10010 Rice, Bovine Liver1577c and GBW 07605 Tea Leaves) were determined by using electrothermal and flame atomic absorption spectrometries. Cd and Sn in sample solutions were determined with electrothermal atomic absorption spectrometry by using palladium (Pd) as a matrix modifier. Pyrolysis and atomization temperatures and pyrolysis times of Cd and Sn in sample solutions were optimized in the absence or presence of Pd. Pyrolysis temperatures of Cd and Sn found in the presence of Pd were 800°C and 1200°C, respectively. Iron, Cu, and Zn in samples were determined by flame atomic absorption spectrometry. The accuracy and precision of the method were validated by determining elements in standard reference materials. Limits of detection for Sn, Cd, Fe, Cu, and Zn were found as 0.66, 0.26, 2.0, 1.9, and 1.2 μg/L, respectively. Concentrations of elements found in samples were compared with maximum values reported by World Health Organization (WHO) and other studies.

Maximization of the photocatalytic degradation of diclofenac using polymeric g-C3N4 by tuning the precursor and the synthetic protocol

A green-oriented synthesis of highly photoactive nano-scaled graphitic carbon nitride (g-C3N4) is presented with water to be utilized as a critical reagent in order to tune desired physicochemical properties, and so, to elevate the photocatalytic activity. The materials’ optimization strategy involved the use of three precursors (melamine, urea or thiourea) and different thermal polycondensation (pyrolysis) durations. The synthesized materials were characterized by SEM, XRD, XPS, N2 sorption, FT-IR, and UV–vis DRS. Their photocatalytic activity against a non-steroidal anti-inflammatory pharmaceutical compound, diclofenac, was evaluated under ultraviolent irradiation, also investigating the influence of pH, photocatalyst dosage/mass and concentration of H2O2. The results revealed that the precursor, pyrolysis time and use of water effect significantly the physicochemical features and the photocatalytic activity. Urea-derived samples showed the highest specific surface areas and smallest crystalline domains, as well as the highest photocatalytic efficiency. The involved mechanisms were examined by exploring the optical properties, the role of the photo-generated radicals and the reactive oxygen species, as well as LC-MS analysis. The Orbitrap high-resolution mass-spectrometry analysis revealed the formation of 26 transformation products governed by different processes such as hydroxylation and further oxidation to keto derivatives and ring opening, decarboxylation/hydroxylation with further oxidation, dichlorination, and lactam formation.