The research trends of metal-organic frameworks in environmental science: a review based on bibliometric analysis

New porous amine-functionalized biochar-based desiccated coconut waste as efficient CO2 adsorbents

Climate change caused by the greenhouse gases CO2 remains a topic of global concern. To mitigate the excessive levels of anthrophonic CO2 in the atmosphere, CO2 capture methods have been developed and among these, adsorption is an especially promising method. This paper presents a series of amine functionalized biochar obtained from desiccated coconut waste (amine-biochar@DCW) for use as CO2 adsorbent. They are ethylenediamine-functionalized biochar@DCW (EDA-biochar@DCW), diethylenetriamine-functionalized biochar@DCW (DETA-biochar@DCW), triethylenetetramine-functionalized biochar@DCW (TETA-biochar@DCW), tetraethylenepentamine-functionalized biochar@DCW (TEPA-biochar@DCW), and pentaethylenehexamine-functionalized biochar@DCW (PEHA-biochar@DCW). The adsorbents were obtained through amine functionalization of biochar and they are characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Brunauer-Emmett-Teller (BET), and thermogravimetric analysis (TGA). The CO2 adsorption study was conducted isothermally and using a thermogravimetric analyzer. From the results of the characterization analyses, a series of amine-biochar@DCW adsorbents had larger specific surface area in the range of 16.2 m2/g-37.1 m2/g as compare to surface area of pristine DCW (1.34 m2/g). Furthermore, the results showed an increase in C and N contents as well as the appearance of NH stretching, NH bending, CN stretching, and CN bending, suggesting the presence of amine on the surface of biochar@DCW. The CO2 adsorption experiment shows that among the amine modified biochar adsorbents, TETA-biochar@DCW has the highest CO2 adsorption capacity (61.78 mg/g) when using a mass ratio (m:m) of biochar@DCW:TETA (1:2). The adsorption kinetics on the TETA-biochar@DCW was best fitted by the pseudo-second model (R2 = 0.9998), suggesting the adsorption process occurs through chemisorption. Additionally, TETA-biochar@DCW was found to have high selectivity toward CO2 gas and good reusability even after five CO2 adsorption-desorption cycles. The results demonstrate the potential of novel CO2 adsorbents based on amine functionalized on desiccated coconut waste biochar.

Global occurrence, drivers, and environmental risks of microplastics in marine environments

With an increasing quantity of plastic waste being discharged into the oceans, marine microplastic (MP) pollution has received widespread attention. However, the global occurrence characteristics, environmental risks, driving factors, and source-sink relationships remain unclear. In this study, we conducted a meta-analysis based on 165 articles about marine MP pollution. It was found that the global marine MP abundance displayed a significant spatial heterogeneity, and the distribution pattern was influenced by offshore distance, population density, and economic development. The morphological characteristics of MPs showed a significant difference between seawater and marine sediment, and small-size MPs (<1 mm) accounted for the majority of all MPs in the marine environment. The environmental risk assessment revealed that most of the marine MP pollution still remains at low concentrations in the global context, with the Polyurethane (PU), Polyacrylonitrile (PAN), and Polyvinyl chloride (PVC) types of MPs showing high environmental-risk contributions. In addition, land-based waste and marine operations, which were considered to be the dominant sources of marine MPs, primarily aggregated at nearshore submarine areas, in the water column, and in the deep-sea bottom environment. This study suggested that the combination of a meta-analysis and Monte Carlo simulation can provide much valuable information regarding the global occurrence characteristics and environmental risks of marine MPs.

Nanocomposites of Copper Trimesinate and Graphene Oxide as Sorbents for the Solid-Phase Extraction of Organic Dyes

A nanocomposite based on graphene oxide and copper trimesinate was obtained by the in situ method. The samples have permanent porosity and a microporous structure with a large surface area corresponding to the adsorption type I. A study of the adsorption properties of the obtained composites with respect to organic dyes (malachite green, indigo carmine, brilliant green, Rose Bengal, crystal violet) showed that adsorption largely depends on the content of graphene oxide in the composites. The complex is an effective sorbent for the extraction of cationic and neutral organic dyes when the content of graphene oxide in the nanocomposite is 20% of the calculated copper trimesinate due to electrostatic forces of interaction. For anionic dyes, the maximum adsorption is achieved when using a composite containing 5% graphene oxide due to the predominance of physical sorption. Experimental results show that the obtained sorbent can be used for extraction in a wide pH range, illustrating the excellent pH window offered by this adsorbent. Kinetics data were properly fitted with the pseudo-second-order model. Equilibrium data were best correlated with the Freundlich model. The process was endothermic and spontaneous in nature. The composite makes it possible to achieve a maximum sorption of 393 mg/g, which is a sufficiently high value for the absorption of dyes.

A γ-cyclodextrin-based metal-organic framework (γ-CD-MOF): a review of recent advances for drug delivery application

The relatively new class of porous material known as metal-organic framework (MOF) exhibits unique features such as high specific surface area, controlled porosity and high chemical stability. Many green synthesis approaches for MOFs have been proposed using biocompatible metal ions and linkers to maximise their use in pharmaceutical fields. The involvement of biomolecules as an organic ligand can act promising because of their biocompatibility. Recently, cyclodextrin metal-organic frameworks (CD-MOFs) represent environmentally friendly and biocompatible characteristics that lead them to biomedical applications. They are regarded as a promising nanocarrier for drug delivery, due to their high specific surface area, high porosity, tuneable chemical structure, and easy fabrication. This review focuses on the unique properties of CD-MOF and the recent advances in methods for the synthesis of these porous structures with emphasis on particle size. Then, the state-of-the-art drug delivery systems with various drugs along with the performance of CD-MOFs as efficient drug delivery systems are presented. Particular emphasis is laid on researches investigating the drug delivery potential of γ-CD-MOF.

Bioenergy research under climate change: a bibliometric analysis from a country perspective

Development of bioenergy will be a key component for meeting increasing energy demands while mitigating global warming. With the intent of identifying current topics of major interest and development of research directions in the field of bioenergy under climate change, we conducted a bibliometric analysis and network analysis from a country perspective based on 3050 articles published since 1999 derived from the Scopus database. The results indicated that USA, UK, and Germany led other countries in terms of number of publications (1006, 366, and 280 articles, respectively) and h-index (greater than 50) in this research area. The USA has also produced a large number of articles in highly respected journals. Compared with developed countries, some developing countries (e.g., China, India, and Brazil) have a larger proportion of publications which are cited less than 10 times and researchers who have academic age of 1 year. The number of publications dealing with some of these research topics coming from developing countries has lagged behind the number of similar publications coming from developed countries. In spite of this, research on sustainable energy systems is still needed for developing countries to further establish feasible systems that can effectively promote global economic development and strengthen climate change mitigation efforts.

Isotherm, kinetic, and thermodynamic studies for dynamic adsorption of toluene in gas phase onto porous Fe-MIL-101/OAC composite

In the present paper, micro-mesoporous Fe-MIL-101/OAC composite using in situ incorporation of Fe-MIL-101 into oxidized activated carbon was synthesized and characterized by XRD, FT-IR, SEM, EDS, and BET techniques. The adsorption performances of toluene onto adsorbents in the gas phase were studied using a laboratory-scale dynamic adsorption system under moist ambience. The toluene adsorption capacity of Fe-MIL-101/OAC composite and Fe-MIL-101 were 127 and 97.6 mg g^-1, severally. Results revealed that the larger pores in micro-mesoporous Fe-MIL-101/OAC enhanced the molecular diffusion rate. The findings indicated that micro-mesoporous structures played key roles in the capture of toluene molecules. The initial toluene concentration positively affected on toluene adsorption capacity while temperature and humidity negatively affected on toluene adsorption capacity. The Langmuir model and the pseudo-second-order kinetics model described better adsorption process of Fe-MIL-101/OAC composite. Thermodynamic findings determined that toluene adsorption over Fe-MIL-101/OAC was spontaneous, exothermic physisorption. The regeneration of the composite was still up to 72.6% after six cycles. The micro-mesoporous Fe-MIL-101/OAC composite proposes a promising support for the high toluene removal for future. Graphical abstract.