The global population growth demands intensification of anthropogenic processes, thus leading to inter alia pollution of both land and aquatic environments with toxic organic compounds. Particularly harmful synthetic compounds are classified as persistent organic pollutants (POPs). Their relatively high chemical resistance resulted in a worldwide ban or strict control on the use of POPs. The majority of POPs were commonly used as pesticides, and unfortunately, some of them are still utilized as an aid in agricultural practices. Therefore, environmental monitoring in terms of reliable detection and quantification of pesticidal POPs is an ever-increasing need. Chemical sensors and adsorption materials crafted for specific pesticide operate on host-guest interactions should provide selectivity and sensitivity, thus leading to the detection of target molecule down to the nanomolar range. This could be achieved with materials exhibiting a very large active surface area, well-defined structure, and high stability. The novel materials studied in that context are metal-organic frameworks (MOFs). The structure of various MOFs can be functionalized to provide desired host-guest interactions. In this mini-review, we critically discuss the application of MOFs for the detection and adsorption of selected pesticides that are classified as POPs according to the Stockholm Convention.
As sulfate-radical (SR)-based advanced oxidation processes are increasingly implemented, Oxone has been frequently-used for generation of SR. While Co3O4 nanoparticle (NP) has been widely-accepted as a promising catalyst for activating Oxone, Co3O4 NPs tend to aggregate in water, losing their reactivity. Thus, many attempts have immobilized Co3O4 NPs on supports, especially carbonaceous substrates, because combination of Co NPs with carbon substrates offers synergistic effects for boosting catalytic activities. Moreover, carbon substrates doped with hetero-atoms (N and S) further increase electron transfer and reactivity. Therefore, it is even promising to immobilize Co NPs onto N/S-doped carbon (NSC) to form Co-embedded NSC (denoted as CoNSC) for enhancing Oxone activation. In this study, a convenient and facile technique is proposed to prepare such a CoNSC via a simple carbonization treatment of a coordination polymer of Co and trithiocyanuric acid (TTCA). The resulting CoNSC exhibits the sheet-like hexagonal morphology with the core-shell configuration, and Co NPs are well-embedded into the N/S-doped carbonaceous matrix, making it an advantageous heterogeneous catalyst for Oxone activation. As Azorubine S (ARS) decolorization is employed as a model reaction of Oxone activation, CoNSC exhibits a higher catalytic activity than pristine Co3O4 and NSC for Oxone activation to decolorize ARS. In comparison to the other reported catalysts, CoNSC also possesses a much lower Ea for ARS decolorization. CoNSC can be also reusable and stable for Oxone activation over multiple cycles without loss of catalytic activity. These features validate that CoNSC is a promising and useful Co-based catalyst for Oxone activation.
To remove harmful volatile organic compounds (VOCs) including 2-butanone (methyl ethyl ketone, MEK) emitted from various industrial plants is very important for the clean air. Also, it is worthwhile to recycle porous spent fluid catalytic cracking (SFCC) catalysts from various petroleum refineries in terms of reducing industrial waste and the reuse of discharged resources. Therefore, Mn and Mn-Cu added SFCC (Mn/SFCC and Mn-Cu/SFCC) catalysts were prepared to compare their catalytic efficiencies together with the SFCC catalyst in the ozonation of 2-butanone. Since the SFCC-based catalysts have a structure similar to that of zeolite Y (Y), the Mn-loaded zeolite Y catalyst (Mn/Y) was also prepared to compare its activity for the removal of 2-butanone and ozone to that of the SFCC-based ones at room temperature. Among the five catalysts of this study (Y, Mn/Y, SFCC, Mn/SFCC, and Mn-Cu/SFCC), the Mn-Cu/SFCC and Mn/SFCC catalysts showed the better catalytic decomposition activity than the others. The increased distributions of the Mn3+ species and the Ovacancy sites in Mn/SFCC and Mn-Cu/SFCC catalysts which could supply more available active sites for the 2-butanone and ozone removal would enhance the catalytic activity of them.
Food waste, a renewable resource, was converted to H2-rich gas via a catalytic steam gasification process. The effects of basic oxides (MgO, CaO, and SrO) with 10 wt% Ni/Al2O3 on the gasification properties of food waste were investigated using a U-shaped gasifier. All catalysts prepared by the precipitation method were analyzed by X-ray diffraction, H2-temperature-programmed reduction, NH3-temperature-programmed desorption, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The Ni/Al2O3 catalyst was reduced incompletely, and low nickel concentrations were detected on the surface of the alumina. The basic oxides minimized the number of acid sites and suppressed the formation of nickel-aluminate (NiAlxOy) phase in catalyst. In addition, the basic oxides shifted nickel-aluminate reduction reaction to lower temperatures. It resulted in enhancing nickel concentration on the catalyst surface and increasing gas yield and hydrogen selectivity. The low gas yield of the Ni/Al2O3 catalyst was attributed to the low nickel concentration on the surface. The maximum gas yield (66.0 wt%) and hydrogen selectivity (63.8 vol%) of the 10 wt% SrO- 10 wt% Ni/Al2O3 catalyst correlated with the highly dispersed nickel on the surface and low acidity. Furthermore, coke deposition during steam gasification varied with the surface acidity of the catalysts and less coke was formed on 10 wt% SrO- 10 wt% Ni/Al2O3 due to efficient tar cracking. This study showed that the steam gasification efficiency of the Ni/Al2O3 catalyst could be improved significantly by the addition of SrO.
Biochar is a carbon-neutral solid fuel and has emerged as a potential candidate to replace coal. Meanwhile, spent coffee grounds (SCGs) are an abundant and promising biomass waste that could be used for biochar production. This study develops a biochar valorization strategy by mixing SCGs with hydrogen peroxide (H2O2) at a weight ratio of 1:0.75 to upgrade SCG biochar. In this dual pretreatment method, the H2O2 oxidative ability at a pretreatment temperature of 105 °C contributes to an increase in the higher heating value (HHV) and carbon content of the SCG biochars. The HHV and carbon content of biochar increase by about 6.5% and 7.8%, respectively, when compared to the unpretreated one under the same conditions. Maximized biochar's HHV derived via the Taguchi method is 30.33 MJkg-1, a 46.9% increase compared to the raw SCG, and a 6.5% increase compared to the unpretreated SCG biochar. The H2O2 concentration is 18% for the maximized HHV. A quantitative identification index of intensity of difference (IOD) is adopted to evaluate the contributive level of H2O2 pretreatment in terms of the HHV and carbon content. IOD increases with increasing H2O2 pretreatment temperature. Before torrefaction, SCGs' IOD pretreated at 50 °C is 1.94%, while that pretreated at 105 °C is 8.06%. This is because, before torrefaction, H2O2 pretreatment sufficiently weakens SCGs' molecular structure, resulting in a higher IOD value. The IOD value of torrefied SCGs (TSCG) pretreated at 105 °C is 10.71%, accounting for a 4.59% increase compared to that pretreated at 50 °C. This implies that TSCG pretreated by H2O2 at 105 °C has better thermal stability. For every 1% increase in IOD of TSCG, the carbon content of the biochar increases 0.726%, and the HHV increases 0.529%. Overall, it is demonstrated that H2O2 is a green and promising pretreatment additive for upgrading SCG biochar's calorific value, and torrefied SCGs can be used as a potential solid fuel to approach carbon neutrality.
While transition metals are useful for activating monopersulfate (MPS) to degrade contaminants, bimetallic alloys exhibit stronger catalytic activities owing to several favorable effects. Therefore, even though Co is an efficient metal for MPS activation, CoFe alloys are even more promising heterogeneous catalysts for MPS activation. Immobilization/embedment of CoFe alloy nanoparticles (NPs) onto hetero-atom-doped carbon matrices appears as a practical strategy for evenly dispersing CoFe NPs and enhancing catalytic activities via interfacial synergies between CoFe and carbon. Herein, N-doped carbon-embedded CoFe alloy (NCCF) is fabricated here to exhibit a unique hollow-engineered nanostructure and the composition of CoFe alloy by using Co-ZIF as a precursor after the facile etching and Fe doping. The Fe dopant embeds CoFe alloy NPs into the hollow-structured N-doped carbon substrate, enabling NCCF to possess the higher mesoscale porosity, active N species as well as more superior electrochemical properties than its analogue without Fe dopants, carbon matrix-supported cobalt (NCCo). Thus, NCCF exhibits a considerably larger activity than NCCo and the benchmark catalyst, Co3O4 NP, for MPS activation to degrade an environmental hormone, dihydroxydiphenyl ketone (DHPK). Besides, NCCF + MPS shows an even lower activation energy for DHPK degradation than literatures, and retains its high efficiency for eliminating DHPK in different water media. DHPK degradation pathway and ecotoxicity assessment are unraveled based on the insights from the computational chemistry, demonstrating that DHPK degradation by NCCF + MPS did not result in the formation of toxic and highly toxic by-products. These features make NCCF a promising heterogeneous catalyst for MPS activation to degrade DHPK.