**1. Introduction**

Rapid industrialization over the past century has resulted in huge demand for power. The most common way to produce power is utilizing fossil fuels, but this causes emission of CO2 which is the main component of greenhouse gas (GHG). The amount of CO2 emitted by different power industries and the energy sector running on fossil fuels constitutes approximately 65% of the total emission of the GHG [1]. As the concern over climate change due to GHGs is increasing all over the world, the reduction in this emission has become an important area of research. Substantial reduction in the emission of CO2 is necessary to follow the agreemen<sup>t</sup> of COP-21. The main outcome of the COP-21, held in Paris in 2015, was the agreemen<sup>t</sup> to maintain the global average temperature rise below 2 ◦C. Further efforts should be pursued to limit this temperature increase below 1.5 ◦C [2].

To reduce emissions, research is being conducted to use renewable resources instead of fossil fuels. One of the interesting methods is the conversion of CO2 into organic compounds using photocatalytic reduction and producing fuel feedstock. Traditional fossil fuels can be used as renewable fuel following this process. Zhou et al. [3] illustrated the use of semiconductor ZnS during photoreduction of CO2 to formate (HCOO-). Sharma et al. [4] portrayed the use of sulfide-based photocatalysts for production of renewable fuel in this method. They used CU3SnS4 as a photocatalyst for reduction of CO2 to CH4. Excellent photocatalytic performance of the sulfide was observed along with good stability. However, no technology is advanced enough to compensate for the reduction in the use of conventional fuels. Though nuclear and renewable energy is predicted to play a significant role in low carbon power production, most of the future power demand is expected to be met by fossil fuels due to safety and other issues [5]. Therefore, it is necessary to think of a way to use conventional fuels for producing power while reducing the emission of CO2. Carbon Capture and Storage (CCS) technology comes here as a rescue. It is the process of capturing the produced CO2 and then storing it in a safe place so that it would not a ffect the environment. International Energy Agency (IEA) has a projection to abate the CO2emission; 17% of this abatement should be done by CCS by 2035 at the lowest cost [6].

To meet the expectation, research is ongoing all over the world to develop new technologies. Currently, the main obstacle in deploying CCS is the huge cost which in e ffect increases the price of electricity. The current estimated cost of capturing CO2 with an established technology is at least \$60/t CO2 [6]. This is too high to make CCS commercially attractive. This huge amount of compensation discourages investment in the energy market. To ge<sup>t</sup> rid of this barrier, research is ongoing mainly in developed countries to keep the cost of carbon capture around \$20/t CO2 captured [6]. In addition to the increased cost associated with CCS, the environmental impact of the methods should also be considered. A reduction in CO2 emission may lead to increasing other emissions a ffecting the environment [7].

Current technologies that are being developed for capturing CO2 can be broadly categorized into the following divisions: (i) Carbon capture with separation, and (ii) Carbon capture without separation. This review focuses on the processes, the current state of the carbon capture technologies, and on identifying the area that demands further research.

### **2. Carbon Capture with Separation**

This process requires technology to separate CO2 from a mixture of di fferent gases. The gas stream may form before or after the combustion. If the gas stream consisting of carbon dioxide is formed before combustion, then it is known as a precombustion carbon capture process. This gas stream consists of mainly CO2 and H2 in this case; otherwise, it is called post combustion carbon capture, where the main constituents of the gas stream are CO2 and N2. Several technologies are currently in use and under development for the separation of CO2 from the gas mixture. Almost all the separation techniques can be applied for both processes.
