The programme in chemistry with environmental and sustainable chemistry is essentially a chemistry degree with added modules of environmental chemistry and sustainable chemistry. These modules are in years 2 and 4 of the degree. The research project that a student does during their final year will be specifically in this field also.
The environmental chemistry looks at causes, effects and remediation of pollution (air, water and soil) while the sustainable chemistry looks at generating replacements for fossil fuels (both as fuels and raw materials) and “green” chemistry (i.e. doing synthesis in more environmentally friendly ways).
There are more details in this link: https://myucd.ucd.ie/course.do?courseID=111
I hope this helps.