Internet of Things (IoT) has become a widespread ubiquitous technology connecting seamlessly the physical world with the internet. The security, trust, and privacy issues are still serious challenges in IoT, as less work has been done on the security aspect. Blockchain technology seems to be the viable solution to maintain security, transparency, auditability, immutability, and privacy in a decentralized manner without any third party intermediary. The main objective of this paper is based on comparative analysis in the existing literature comprising of consensus mechanisms, smart contracts, architectures, service platforms, and application use cases in blockchain-based IoT (BIoT). This paper presents a comprehensive review and the flow of information starting from: vast IoT applications and the main challenges in its adoption, integration of blockchain with IoT and applications. Finally, some important challenges were discussed in order to have a novel network of IoT nodes having security, privacy, transparency throughout the communication medium.