Let's start with the definitions
Hadoop is an open source, scalable and fault tolerant framework from ASF - Apache Software foundation and its framework is in Java. By Open source it means it is available for free to everyone and its source can also be changed as per the requirements.
Hadoop processes Big data on a cluster of commodity hardware. If a certain functionality does not work properly or fulfill your need, you can change it accordingly.
Now NoSQL on the other hand NoSQL is a type of database management system which is used to store structured, semi-structured, as well as unstructured data. It is schema-less.
Hadoop Supports a lot of NoSQL databases: Hbase and Cassandra are the top choices when it comes to integrating nosql databases with Hadoop Framework.
Hope this helps.