Energy and environmental topics are tightly linked and cannot be understood without each other especially under the stringent legislation policies and environmental social awareness. Both are considered hot scientific research topics with more than 5 million documents archived on the Web of Science until the year 2019. Based on a vast number of publications, this work proposes a bibliometrics approach to derive scientific connections and to envision future research trends based on semantic analysis and networking landscape representations. The study found that research trends have evolved from a theoretical approach to a more general point of view related to the optimization and integration of renewable energy applications. In particular, the whole energy value chain from harvesting to consumption (including distribution, storage, management and conservation) is the trendiest area of current research and especially its application to the building environment. Those research areas are strongly supported by the recent developments on the internet of things and wireless sensor networks.

Diversified human activities and inappropriate economic growth strategies have induced a trade-off between economic growth and environmental degradation worldwide. Consequently, the aggravating environmental concerns have warranted regulations to be enforced for safeguarding the welfare of the global environment. However, the effectiveness of such environmental regulations in reducing environmental deterioration has received equivocal empirical evidence in the literature. Against this backdrop, this study investigates the influence of environmental regulations on the ecological footprints in the context of the Next Eleven countries between 1990 and 2016. The results from the econometric analysis, controlling for cross-sectional dependency issues in the data, reveal that the existing environmental regulations legislated in the Next Eleven countries are ineffective in reducing the ecological footprints of these nations. Besides, greater energy consumption and openness to international trade are found to boost ecological footprints. Moreover, the Environmental Kuznets Curve hypothesis is also authenticated for the panel of the Next Eleven nations. The country-specific findings indicate that energy consumption anonymously degraded the environment in all the eleven nations, while heterogeneous impacts of environmental regulations, economic growth and international trade on the environment are ascertained. Hence, these findings, in a nutshell, recommend the Next Eleven nations to strengthen and enforce the environmental regulations, adopt sustainable economic growth policies, reduce fossil fuel dependency and participate in sustainable trade to ensure environmental sustainability.

The use of alternative energy sources is nearly the only way to meet the energy needs of people worldwide caused by the exhaustion of natural fuel sources. Currently, solar energy is the most affordable and environmentally sustainable energy resource. However, the efficiency of the existing solar collectors is below 50%. There are many technological approaches to increase the heat transfer efficiency of solar collectors, which imply the enhancement of solar radiation uptake. The efficiency of solar collectors was also found dependent upon the properties of the working liquid. Nanofluids are used to improve the thermal properties of solar collectors as they are characterized by good radiation absorption performance. This paper examines the thermal performance of different nanofluids used to collect solar energy at the volumetric flow rate ranging from 50 to 100 ml/h using a GALMET heat exchanger. The examined nanofluids are aqueous solutions composed of Al₂O₃, SiO₂, TiO₂, and graphene nanoparticles (0.500…2wt.%). With these nanofluids, direct absorption solar collectors (DASCs) demonstrated efficiency improvements of up to 5%. The effect of flow hydrodynamics on heat transfer capacity and thermal efficiency of solar collectors has been studied. The thermal performances of nanofluids were as follows: graphene-based, 10.755 kJ/m; TiO₂-based, 9.414 kJ/m²; SiO₂-based, 7.467 kJ/m²; and Al₂O₃-based, 5.714 kJ/m². The efficiencies of solar collectors using these nanofluids as a working fluid were 64%, 59%, 57%, and 52%, respectively. The multi-factor cluster analysis revealed that graphene nanofluid was the most efficient choice.

Recent environmental regulations have urged refiners to decrease NO _x emissions related to fuels particularly used in marine transportation. To this, hydrodenitrogenation (HDN) of Iranian Vacuum Bottom (IVB), as one of the most abundant but problematic effluents of Iranian refineries used for marine applications, was evaluated for the very first time via batch hydrotreating procedure over a commercial NiMo catalyst. First, the feed material's physicochemical properties were fully analyzed using several analytic techniques such as CHNS, micro-carbon residue, and TGA. Process chemistry of the HDN and mild hydrocracking (MHC) processes was studied systematically following an L₉-assisted design of experiment (Taguchi method) whereby temperature (350–410 °C), reaction time (1–3 h), oil content:catalyst ratio (1.5–2.5), and H₂ initial pressure (3.0–7.0 MPa) were considered as control factors. Adding to the highly pre-pressurized medium (H₂ initial pressure of 7.0 MPa) at elevated temperature (410 °C) as the most favorable condition for HDN and MHC reactions, results also highlighted a few critical interactions between the operating variables. The key was simultaneous saturation and decomposition of the highly aromatic nature of IVB, under which 65.3% of nitrogen impurities were taken out of the feed’s recalcitrant network. Notably, we took advantage of some well-known analytic techniques like Sim Dis and GC–MS to shed light on the origin of the N-containing compounds in the feed material and physicochemical characteristics of liquid products. These fuel-related analyses provided us a deeper look into the process chemistry using thermodynamic and kinetic backgrounds.

The current work deals with the process intensification of esterification reaction via ultrasonic (US) and microwave (MW) irradiations using the cheapest feedstock, such as Palm Fatty Acid Distillate (PFAD). Systematic studies have been done by conventional methods to find the optimum parameters, such as molar ratio of PFAD to methanol, temperature, type of catalyst, and catalyst loading. In order to enhance the rate of reaction, experiments were carried out using approaches based on ultrasound and microwave irradiations at optimal parameters obtained from the conventional approach. Significant enhancement in extent of equilibrium conversion and rate of reaction is observed in the presence of microwave irradiation than any other method used in the current study. The maximum reduction in acid value obtained using MW irradiation, US irradiation, and conventional approaches was 98.8% (for 25 min of reaction time), 97.8% (for 150 min of reaction time), and 97.6% (for 180 min of reaction time), respectively. The kinetic rate constants (activation energy) for the reaction using MW irradiation, US irradiation, and conventional approach were 0.7089 (9.6 × 10⁴ kJ/mg), 0.2063 (1.7 × 10⁵ kJ/mg), and 0.1629 (2.1 × 10⁵ kJ/mg) l/mol/min, respectively.